Novel onium salts, photoacid generators, resist compositions, and patterning process

ABSTRACT

Onium salts of arylsulfonyloxynaphthalenesulfonate anions with iodonium or sulfonium cations are novel. A chemically amplified resist composition comprising the onium salt as a photoacid generator is suited for microfabrication, especially by deep UV lithography because of many advantages including improved resolution, improved focal latitude, minimized line width variation or shape degradation even on long-term PED, minimized debris after coating, development and peeling, and improved pattern profile after development.

[0001] This invention relates to novel onium salts, photoacid generatorsfor resist compositions, resist compositions comprising the photoacidgenerators, and a patterning process using the same. The resistcompositions, especially chemical amplification type resist compositionsare sensitive to such radiation as UV, deep UV, electron beams, x-rays,excimer laser beams, γ-rays, and synchrotron radiation and suitable forthe microfabrication of integrated circuits.

BACKGROUND OF THE INVENTION

[0002] While a number of efforts are currently being made to achieve afiner pattern rule in the drive for higher integration and operatingspeeds in LSI devices, deep-ultraviolet lithography is thought to holdparticular promise as the next generation in microfabricationtechnology.

[0003] One technology that has attracted a good deal of attentionrecently utilizes as the deep UV light source a high-intensity KrFexcimer laser, especially an ArF excimer laser featuring a shorterwavelength. There is a desire to have a microfabrication technique offiner definition by combining exposure light of shorter wavelength witha resist material having a higher resolution.

[0004] In this regard, the recently developed, acid-catalyzed, chemicalamplification type resist materials are expected to comply with the deepUV lithography because of their many advantages including highsensitivity, resolution and dry etching resistance. The chemicalamplification type resist materials include positive working materialsthat leave the unexposed areas with the exposed areas removed andnegative working materials that leave the exposed areas with theunexposed areas removed.

[0005] In chemical amplification type, positive working, resistcompositions to be developed with alkaline developers, an alkali-solublephenol or a resin and/or compound in which carboxylic acid is partiallyor entirely protected with acid-labile protective groups (acid labilegroups) is catalytically decomposed by an acid which is generated uponexposure, to thereby generate the phenol or carboxylic acid in theexposed area which is removed by an alkaline developer. Also, in similarnegative working resist compositions, an alkali-soluble phenol or aresin and/or compound having carboxylic acid and a compound(crosslinking agent) capable of bonding or crosslinking the resin orcompound under the action of an acid are crosslinked with an acid whichis generated upon exposure whereby the exposed area is converted to beinsoluble in an alkaline developer and the unexposed area is removed bythe alkaline developer.

[0006] On use of the chemical amplification type, positive working,resist compositions, a resist film is formed by dissolving a resinhaving acid labile groups as a binder and a compound capable ofgenerating an acid upon exposure to radiation (to be referred to asphotoacid generator) in a solvent, applying the resist solution onto asubstrate by a variety of methods, and evaporating off the solventoptionally by heating. The resist film is then exposed to radiation, forexample, deep UV through a mask of a predetermined pattern. This isoptionally followed by post-exposure baking (PEB) for promotingacid-catalyzed reaction. The exposed resist film is developed with anaqueous alkaline developer for removing the exposed area of the resistfilm, obtaining a positive pattern profile. The substrate is then etchedby any desired technique. Finally the remaining resist film is removedby dissolution in a remover solution or ashing, leaving the substratehaving the desired pattern profile.

[0007] The chemical amplification type, positive working, resistcompositions adapted for KrF excimer lasers generally use a phenolicresin, for example, polyhydroxystyrene in which some or all of thehydrogen atoms of phenolic hydroxyl groups are protected with acidlabile protective groups. Onium salts such as iodonium salts andsulfonium salts, bissulfonyldiazomethane compounds, andN-sulfonyloxyimide compounds are typically used as the photoacidgenerator. If necessary, there are added additives, for example, adissolution inhibiting or promoting compound in the form of a carboxylicacid and/or phenol derivative having a molecular weight of up to 3,000in which some or all of the hydrogen atoms of carboxylic acid and/orphenolic hydroxyl groups are protected with acid labile groups, acarboxylic acid compound for improving dissolution characteristics, abasic compound for improving contrast, and a surfactant for improvingcoating characteristics.

[0008] Onium salts as shown below are advantageously used as thephotoacid generator in chemical amplification type resist compositions,especially chemical amplification type, positive working, resistcompositions adapted for KrF excimer lasers because they provide a highsensitivity and resolution and are free from storage instability asfound with the N-sulfonyloxyimide photoacid generators.

[0009] Since a finer pattern size is required, even the use of suchphotoacid generators gives rise to many problems including lowresolution, low environmental stability, and the formation of insolubleor difficultly soluble foreign matter upon development with an alkalinedeveloper or removal of the resist with a solvent.

[0010] Of these problems, improvements in resolution are made byintroducing into a resin acid labile groups which are more prone toscission by an acid, or adding a basic compound, or modifying processingconditions.

[0011] It is known from JP-A 8-123032 to use two or more photoacidgenerators in a resist material. JP-A 11-72921 discloses the use of aradiation-sensitive acid generator comprising in admixture a compoundwhich generates a sulfonic acid having at least three fluorine atomsupon exposure to radiation and a compound which generates a fluorineatom-free sulfonic acid upon exposure to radiation, thereby improvingresolution without inviting nano-edge roughness and film surfaceroughening. However, we empirically found that these resist compositionsare unsatisfactory in resolution and in the effect of eliminating theforeign matter on the pattern upon development.

[0012] For the purpose of improving the resolution uponmicrofabrication, JP-A 6-148889 discloses a positive photosensitivecomposition comprising a polyfunctional enol ether compound and analkali-soluble resin as typified by polyhydroxystyrene, which arethermally crosslinked on a substrate, followed by exposure to radiationand PEB to provide a desired pattern. JP-A 6-266112 discloses aphotosensitive resist composition comprising a photosensitive acidgenerator and a polymer composed of hydroxystyrene and an acrylateand/or methacrylate. These compositions are unsatisfactory in resolutionand pattern profile. Substantial sliming upon post-exposure delay (PED)is also a problem.

[0013] The environmental stability is generally divided into twocategories. One environmental stability is related to the deactivationof a photo-generated acid by an air-borne base above the resist film ora base beneath the resist film and on the substrate. This phenomenon isoften seen when a photoacid generator capable of generating an acidhaving a high acid strength is used. It is expected that this problem issolved by introducing into the resin acid labile groups which are moreprone to scission by acid or by lowering or weakening the acid strengthof the photo-generated acid. The other environmental stability is thatwhen the period from exposure to post-exposure baking (PEB) isprolonged, which is known as post-exposure delay (PED), thephoto-generated acid diffuses in the resist film so that aciddeactivation may occur when the acid labile groups are less susceptibleto scission and acid decomposition may take place when the acid labilegroups are susceptible to scission, often inviting a change of thepattern profile in either case. For example, this invites a sliming ofthe line width in the unexposed area in the case of chemicalamplification type, positive working, resist compositions having acidlabile groups, typically acetal groups.

[0014] As mentioned above, for achieving a high resolution, the resinshould have introduced therein acid labile groups which are more proneto scission, and the photoacid generator should desirably generate aless diffusible acid. The less diffusible acids under investigation arealkylsulfonic acids such as 10-camphorsulfonic acid. The alkylsulfonicacids, however, are weak in acid strength as compared with theconventionally used fluorinated alkylsulfonic acids and arylsulfonicacids, and such low acid strength must be compensated for by thequantity of acid. In order that a more quantity of acid be generated,the exposure time must be increased, often leading to poor productivity.

[0015] Addressing this problem, JP-A 6-199770, 9-244234 and 9-258435disclose resist compositions using photoacid generators in the form ofarylsulfonic acids having an alkyl, carbonyl or carboxylate groupintroduced therein.

[0016] However, we empirically found that the direct introduction of acarbonyl or carboxylate group into a benzene ring is effective forsuppressing the diffusion of the generated acid, but undesirablyincreases the light absorption near 248 nm of the photoacid generatorand that the introduction of an alkyl group can undesirably leaveforeign matter upon development.

[0017] With respect to the foreign matter left upon alkali developmentand/or removal of the resist film with a solvent, a variety of factorsincluding photo-decomposed products of the photoacid generator,non-decomposed compound (that is the photoacid generator as such) andlow soluble resin are considered, and none of these factors have beenidentified responsible. However, the foreign matter is presumablycorrelated to the solubility or affinity of the photoacid generator inthe developer (aqueous solution) or remover solvent and the solubilityor affinity thereof in the resin.

[0018] The photoacid generator in resist material is required to meet afully high solubility in (or compatibility with) a resist solvent and aresin, good storage stability, non-toxicity, effective coating, awell-defined pattern profile, PED stability, and no foreign matter leftduring pattern formation after development and upon resist removal. Theconventional photoacid generators, especially those photoacid generatorscapable of generating alkylsulfonic acids and arylsulfonic acids do notmeet all of these requirements.

[0019] As the pattern of integrated circuits becomes finer in thesedays, a higher resolution is, of course, required, and the problems ofline width variation by PED and foreign matter after development andresist removal become more serious.

SUMMARY OF THE INVENTION

[0020] An object of the invention is to provide a novel onium salt foruse in a resist composition, especially of the chemical amplificationtype, such that the resist composition ensures a high resolution and awell-defined pattern profile after development and minimizes the foreignmatter left after development and resist removal. Another object of theinvention is to provide a photoacid generator for resist compositions, aresist composition comprising the photoacid generator, and a patterningprocess using the same.

[0021] We have found that by using an onium salt of the general formula(1), especially a sulfonium salt of the general formula (1a) or (1a′) oran iodonium salt of the general formula (1b), to be defined below, asthe photoacid generator in a resist composition, there are achieved anumber of advantages including storage stability, effective coating,minimized line width variation or shape degradation during long-termPED, minimized foreign matter left after coating, development and resistremoval, a well-defined pattern profile after development, and a highresolution enough for microfabrication, especially by deep UVlithography.

[0022] When the onium salt of formula (1) is used in a chemicalamplification type resist composition as the photoacid generator, aresist image featuring a high resolution and a wide range of focal depthis obtainable due to the low diffusing effect of sulfonate anions. Atthe same time, the degradation of a pattern profile by PED is minimized,and the foreign matter left after alkali development and resist removalis minimized due to the polarity of sulfonium or iodonium salt.

[0023] Therefore, the invention provides onium salts, photoacidgenerators, resist compositions and a patterning process as definedbelow.

[0024] In one aspect, the invention provides an onium salt of thefollowing general formula (1).

[0025] Herein R¹ is a substituted or unsubstituted aryl group of 6 to 14carbon atoms, R² which may be the same or different is hydrogen or asubstituted or unsubstituted, straight, branched or cyclic alkyl groupof 1 to 6 carbon atoms, R⁰ is a hydroxyl, alkoxy, halogen or nitrogroup, p is 1 or 2, q and r each are 0, 1 or 2, R³ which may be the sameor different is a substituted or unsubstituted, straight, branched orcyclic alkyl group of 1 to 10 carbon atoms or substituted orunsubstituted aryl group of 6 to 14 carbon atoms, M is a sulfur oriodine atom, and “a” is equal to 3 when M is sulfur and equal to 2 whenM is iodine.

[0026] A preferred embodiment is a sulfonium salt of the followinggeneral formula (1a).

[0027] Herein R¹, R², R⁰, p, q, r and R³ are as defined above.

[0028] Another preferred embodiment is a sulfonium salt of the followinggeneral formula (1a′).

[0029] Herein R¹, R², R⁰, p, q, r and R³ are as defined above, G is anacid labile group having an oxygen atom attached thereto or R²O— or(R²)₂N—, g is an integer of 0 to 4, h is an integer of 1 to 5, g+h=5, eis an integer of 1 to 3, f is an integer of 0 to 2, and e+f=3.

[0030] Preferably, the acid labile group is selected from amongtert-butoxy, tert-amyloxy, tert-butoxycarbonyloxy,tert-butoxycarbonylmethyloxy, 1-ethoxyethoxy, tetrahydropyranyloxy,tetrahydrofuranyloxy, trimethylsilyloxy, and 1-ethylcyclopentyloxygroups.

[0031] A further preferred embodiment is a iodonium salt of thefollowing general formula (1b).

[0032] Herein R¹, R², R⁰, p, q, and r are as defined above.

[0033] In a second aspect, the invention provides a photoacid generatorfor a chemical amplification type resist composition comprising theonium salt defined above.

[0034] In a third aspect, the invention provides

[0035] a chemical amplification type resist composition comprising (A) aresin which changes its solubility in an alkaline developer under theaction of an acid, and (B) the aforementioned photoacid generator whichgenerates an acid upon exposure to radiation; or

[0036] a chemical amplification type resist composition comprising (A) aresin which changes its solubility in an alkaline developer under theaction of an acid, (B) the aforementioned photoacid generator whichgenerates an acid upon exposure to radiation, and (C) a compound capableof generating an acid upon exposure to radiation, other than component(B). Preferably, the resin (A) has such substituent groups having C—O—Clinkages that the solubility in an alkaline developer changes as aresult of scission of the C—O—C linkages under the action of an acid.The resist composition may further include (D) a basic compound and/or(E) a carboxyl group-containing compound.

[0037] In a fourth aspect, the invention provides a process for forminga pattern, comprising the steps of applying the aforementioned resistcomposition onto a substrate to form a coating; heat treating thecoating and exposing the coating to high energy radiation with awavelength of up to 300 nm or electron beam through a photo-mask;optionally heat treating the exposed coating, and developing the coatingwith a developer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0038] Onium Salt

[0039] In the first aspect, the invention provides a novel onium salthaving a substituted or unsubstitutedarylsulfonyloxynaphthalenesulfonate anion of the following generalformula (1).

[0040] Herein R¹ is a substituted or unsubstituted aryl group of 6 to 14carbon atoms, R² which may be the same or different is hydrogen or asubstituted or unsubstituted, straight, branched or cyclic alkyl groupof 1 to 6 carbon atoms, R⁰ is a hydroxyl group, alkoxy group, halogenatom or nitro group, p is 1 or 2, q and r each are 0, 1 or 2, R³ whichmay be the same or different is a substituted or unsubstituted,straight, branched or cyclic alkyl group of 1 to 10 carbon atoms orsubstituted or unsubstituted aryl group of 6 to 14 carbon atoms, M is asulfur or iodine atom, and “a” is equal to 3 when M is sulfur and equalto 2 when M is iodine.

[0041] Specifically, the invention provides a novel sulfonium salthaving a substituted or unsubstitutedarylsulfonyloxynaphthalenesulfonate anion of the following generalformula (1a) or (1a′).

[0042] Herein R³, R², R⁰, p, q, r and R³ are as defined above.

[0043] Herein R¹, R², R⁰, p, q, r and R³ are as defined above.

[0044] G is an acid labile group having an oxygen atom attached theretoor R²O— or (R²)₂N—, g is an integer of 0 to 4, h is an integer of 1 to5, g+h=5, e is an integer of 1 to 3, f is an integer of 0 to 2, ande+f=3.

[0045] Specifically, the invention also provides a novel iodonium salthaving a substituted or unsubstitutedarylsulfonyloxynaphthalenesulfonate anion of the following generalformula (1b).

[0046] Herein R¹, R², R⁰, p, q and r are as defined above.

[0047] In formulae (1), (1a), (1a′) and (1b), R′, which may be the sameor different, stands for substituted or unsubstituted aryl groups of 6to 14 carbon atoms. Illustrative, non-limiting examples include phenyl,4-methylphenyl, 4-ethylphenyl, 4-methoxyphenyl, 4-tert-butylphenyl,2,4-dimethylphenyl, 2,4,6-trimethylphenyl, 2,4,6-triisopropylphenyl,1-naphthyl and 2-naphthyl.

[0048] In formulae (1), (1a), (1a′) and (1b), R², which may be the sameor different, stands for hydrogen or straight, branched or cyclic alkylgroups of 1 to 6 carbon atoms. Illustrative, non-limiting, examplesinclude straight, branched or cyclic alkyl groups such as methyl, ethyl,n-propyl, sec-propyl, n-butyl, sec-butyl, iso-butyl, tert-butyl,n-pentyl, sec-pentyl, cyclopentyl, n-hexyl, and cyclohexyl as well assubstituted alkyl groups such as 2-oxopropyl, 2-oxocyclopentyl,2-oxocyclohexyl, 2-hydroxycyclopentyl and 2-hydroxycyclohexyl.

[0049] In formulae (1), (1a), (1a′) and (1b), R⁰ stands for a hydroxyl,alkoxy group of 1 to 6 carbon atoms, halogen atom or nitro group.Illustrative, non-limiting examples include hydroxyl groups, straight,branched or cyclic alkoxy groups such as methoxy, ethoxy, n-propoxy,sec-propoxy, n-butoxy, sec-butoxy, iso-butoxy, tert-butoxy, n-pentyloxy,sec-pentyloxy, cyclopentyloxy, n-hexyloxy, and cyclohexyloxy, fluorine,chlorine, bromine and iodine atoms, and nitro groups.

[0050] In formulae (1), (1a), (1a′) and (1b), R³, which may be the sameor different, stands for substituted or unsubstituted, straight,branched or cyclic alkyl groups of 1 to 10 carbon atoms or substitutedor unsubstituted aryl groups of 6 to 14 carbon atoms. Illustrative,non-limiting, examples include straight, branched or cyclic alkyl groupssuch as methyl, ethyl, n-propyl, sec-propyl, n-butyl, sec-butyl,iso-butyl, tert-butyl, n-pentyl, sec-pentyl, cyclopentyl, n-hexyl, andcyclohexyl; substituted alkyl groups such as 2-oxopropyl,2-oxocyclopentyl, 2-oxocyclohexyl, 2-hydroxycyclopentyl and2-hydroxycyclohexyl; and aryl groups such as phenyl, 4-methylphenyl,4-ethylphenyl, 4-methoxyphenyl, 4-tert-butylphenyl, 4-tert-butoxyphenyl,4-cyclohexylphenyl, 4-cyclohexyloxyphenyl, 2,4-dimethylphenyl,2,4,6-trimethylphenyl, 2,4,6-triisopropylphenyl,3,4-bis(tert-butoxy)phenyl, 4-dimethylaminophenyl, 1-naphthyl and2-naphthyl.

[0051] The letter p is 1 or 2, and q and r each are 0, 1 or 2. Informula (1), M is a sulfur or iodine atom. The letter “a” is equal to 3when M is sulfur and equal to 2 when M is iodine.

[0052] In formula (1a′), G is an acid labile group having an oxygen atomattached thereto or an alkoxy group: R²O— or a group: (R²)₂N— wherein R²is as defined above. The acid labile group having an oxygen atomattached thereto may be selected from the acid labile groups onhigh-molecular weight compounds or resins to be described later, thoughis not limited thereto. Among others, tert-butoxy, tert-amyloxy,tert-butoxycarbonyloxy, tert-butoxycarbonylmethyloxy, 1-ethoxyethoxy,tetrahydropyranyl, tetrahydrofuranyl, trimethylsilyloxy, and1-ethylcyclopentyloxy are preferred.

[0053] The onium salts of formulae (1), (1a), (1a′) and (1b) accordingto the invention are salts of arylsulfonyloxynaphthalenesulfonate anionswith iodonium or sulfonium cations. Exemplary combinations of anionswith cations are given below.

[0054] Examples of the sulfonate anion include4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-(phenylsulfonyloxy)naphthalene-1-sulfonate,8-(phenylsulfonyloxy)naphthalene-1-sulfonate,5-(phenylsulfonyloxy)naphthalene-1-sulfonate,6-(phenylsulfonyloxy)naphthalene-2-sulfonate,4-(2-naphthylsulfonyloxy)naphthalene-1-sulfonate,8-(2-naphthylsulfonyloxy)naphthalene-1-sulfonate,5-(2-naphthylsulfonyloxy)naphthalene-1-sulfonate,6-(2-naphthylsulfonyloxy)naphthalene-2-sulfonate,6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,6,7-bis(phenylsulfonyloxy)naphthalene-2-sulfonate,5,7-dinitro-8-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate, and5,7-dinitro-8-(phenylsulfonyloxy)naphthalene-2-sulfonate.

[0055] Exemplary iodonium cations include diphenyliodonium,bis(4-tert-butylphenyl)odonium, 4-methoxyphenylphenyliodonium,4-ethoxyphenylphenyliodonium, and 4-tert-butoxy-phenylphenyliodonium,with the diphenyliodonium and bis(4-tert-butylphenyl)iodonium arepreferred.

[0056] Exemplary sulfonium cations include triphenyl-sulfonium,4-hydroxyphenyldiphenylsulfonium, (4-methyl-phenyl)diphenylsulfonium,bis(4-methylphenyl)-phenylsulfonium, tris(4-methylphenyl)sulfonium,(4-methoxyphenyl)diphenylsulfonium, bis(4-methoxyphenyl)phenylsulfonium,tris(4-methoxyphenyl)sulfonium, (4-tert-butylphenyl)diphenylsulfonium,bis(4-tert-butylphenyl)phenylsulfonium,tris(4-tert-butylphenyl)sulfonium,(4-tert-butoxyphenyl)diphenylsulfonium,bis(4-tert-butoxyphenyl)phenylsulfonium,tris(4-tert-butoxyphenyl)sulfonium,(3-tert-butoxyphenyl)diphenylsulfonium,bis(3-tert-butoxyphenyl)phenylsulfonium,tris(3-tert-butoxyphenyl)sulfonium,(3,4-di-tert-butoxyphenyl)diphenylsulfonium,bis(3,4-di-tert-butoxyphenyl)phenylsulfonium,tris(3,4-di-tert-butoxyphenyl)sulfonium,diphenyl(4-thiophenoxyphenyl)sulfonium,(4-tert-butoxycarbonyl-methyloxyphenyl)diphenylsulfonium,tris(4-tert-butoxy-carbonylmethyloxyphenyl)sulfonium,(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,tris(4-dimethylamino-phenyl)sulfonium, 2-naphthyldiphenylsulfonium,dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium,4-methoxyphenyldimethylsulfonium, dimethylphenylsulfonium,diphenylmethylsulfonium, trimethylsulfonium,2-oxocyclo-hexylcyclohexylmethylsulfonium,2-oxocyclohexyl-methylphenylsulfonium,2-oxocyclopentyl-methyl-phenylsulfonium,2-oxocyclopropyl-methyl-phenylsulfonium, and tribenzyl-sulfonium. Ofthese, triphenylsulfonium, 4-tert-butoxy-phenyldiphenylsulfonium,dimethylphenylsulfonium, and 4-tert-butylphenyldiphenylsulfonium arepreferred.

[0057] Especially useful onium salts are: triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,triphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,triphenylsulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-tert-butoxyphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-tert-butoxyphenyldiphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-tert-butoxyphenyldiphenylsulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-tert-butoxyphenyldiphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-methylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-methylphenyl)sulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-methylphenyl)sulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-methylphenyl)sulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-methylphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-methylphenyldiphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-methylphenyldiphenylsulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-methylphenyldiphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-tert-butylphenyl)sulfonium4-(phenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-tert-butylphenyl)sulfonium8-(phenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-tert-butylphenyl)sulfonium5-(phenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-tert-butylphenyl)sulfonium6-(phenylsulfonyloxy)naphthalene-2-sulfonate, triphenylsulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-tert-butoxyphenyldiphenylsulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-methylphenyl)sulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-tert-butylphenyl)sulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,bis(4-tert-butylphenyl)iodonium4-(phenylsulfonyloxy)naphthalene-1-sulfonate,bis(4-tert-butylphenyl)iodonium8-(phenylsulfonyloxy)naphthalene-1-sulfonate,bis(4-tert-butylphenyl)iodonium5-(phenylsulfonyloxy)naphthalene-1-sulfonate,bis(4-tert-butylphenyl)iodonium6-(phenylsulfonyloxy)naphthalene-2-sulfonate, andbis(4-tert-butylphenyl)iodonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate.

[0058] The onium salts can be synthesized by the following methodalthough the synthesis method is not limited thereto.

[0059] The sulfonyloxynaphthalenesulfonic acid of the onium saltaccording to the invention may be obtained by condensing naphtholsulfonic acid with a sulfonyl halide or sulfonic anhydride or bysulfonating a naphthyl sulfonate.

[0060] In condensing naphtholsulfonic acid with a sulfonyl halide orsulfonic anhydride, basic conditions must be employed.

[0061] In condensing a naphthol with sulfonyl chloride, reaction is alsopreferably carried out under basic conditions. Sulfonating can beeffected by a conventional method using sulfur trioxide, sulfuric acid,chlorosulfonic acid, amidosulfuric acid or the like.

[0062] Illustrative, non-limiting examples of the naphtholsulfonic acidused herein include 4-hydroxy-1-naphthalenesulfonic acid,8-hydroxy-1-naphthalenesulfonic acid, 5-hydroxy-1-naphthalenesulfonicacid, 6-hydroxy-2-naphthalenesulfonic acid,6,7-dihydroxy-2-naphthalenesulfonic acid,5,7-dinitro-8-hydroxy-2-naphthalenesulfonic acid and alkali metal saltsthereof. Illustrative, non-limiting examples of the sulfonyl halide orsulfonic anhydride used herein include benzenesulfonyl chloride,4-toluenesulfonyl chloride, 4-methoxybenzenesulfonyl chloride,4-fluorobenzenesulfonyl chloride, 2,4,6-trimethylbenzenesulfonylchloride, 1-naphthylsulfonyl chloride, 2-naphthylsulfonyl chloride andacid anhydrides of the foregoing sulfonyl chlorides.

[0063] The process for the synthesis of corresponding sulfonium andiodonium salts is not critical although the preferred anions are halideions and alkylsulfonic acids having a lower acid strength thanarylsulfonic acids. It is noted that a sulfonium salt having a strongacid such as trifluoromethanesulfonic acid is difficult to effect anionexchange with the above-synthesized sulfonyloxynaphthalenesulfonic acid.The sulfonium and iodonium salts can be synthesized according to theteachings of The Chemistry of Sulfonium Group, Part 1, John-Wiley & Sons(1981), Advanced Photochemistry, vol. 17, John-Wiley & Sons (1992), J.Org. Chem., 1988, 53, 5571-5573, JP-A 7-25846, and JP-A 8-311018.

[0064] The anion exchange may be effected in an alcoholic solvent suchas methanol or ethanol or a two-layer system such asdichloromethane-water.

[0065] The onium salts of formula (1), (1a), (1a′) or (1b) find best useas the photoacid generator in resist materials, especially chemicalamplification type resist materials although the application of theonium salts is not limited thereto. The invention provides resistcompositions comprising onium salts of formula (1), (1a), (1a′) or (1b)as the photoacid generator.

[0066] Resist Composition

[0067] The onium salts of formula (1), (1a), (1a′) or (1b) are useful asthe photoacid generator in chemical amplification type resistcompositions. The resist compositions may be either positive or negativeworking.

[0068] The resist compositions of the invention include a variety ofembodiments,

[0069] 1) a chemically amplified positive working resist compositioncomprising (A) a resin which changes its solubility in an alkalinedeveloper under the action of an acid, (B) an onium salt capable ofgenerating an acid upon exposure to radiation of formula (1), (1a),(1a′) or (1b), and (G) an organic solvent;

[0070] 2) a chemically amplified positive working resist compositionof 1) further comprising (C) a photoacid generator capable of generatingan acid upon exposure to radiation other than component (B);

[0071] 3) a chemically amplified positive working resist compositionof 1) or 2) further comprising (D) a basic compound;

[0072] 4) a chemically amplified positive working resist compositionof 1) to 3) further comprising (E) an organic acid derivative;

[0073] 5) a chemically amplified positive working resist compositionof 1) to 4) further comprising (F) a compound with a molecular weight ofup to 3,000 which changes its solubility in an alkaline developer underthe action of an acid;

[0074] 6) a chemically amplified negative working resist compositioncomprising (B) an onium salt capable of generating an acid upon exposureto radiation of formula (1), (1a), (1a′) or (1b), (H) an alkali-solubleresin, (I) an acid crosslinking agent capable of forming a crosslinkedstructure under the action of an acid, and (G) an organic solvent;

[0075] 7) a chemically amplified negative working resist composition of6) further comprising (C) another photoacid generator;

[0076] 8) a chemically amplified negative working resist composition of6) or 7) further comprising (D) a basic compound; and

[0077] 9) a chemically amplified negative working resist composition of6), 7) or 8) further comprising (J) an alkali-soluble compound with amolecular weight of up to 2,500; but are not limited thereto.

[0078] Moreover, the invention provides a process for forming a pattern,comprising the steps of applying the resist composition defined aboveonto a substrate to form a coating; heat treating the coating andexposing the coating to high energy radiation with a wavelength of up to300 nm or electron beam through a photo-mask; optionally heat treatingthe exposed coating, and developing the coating with a developer.

[0079] Now the respective components of the resist composition aredescribed in detail.

[0080] Component (G)

[0081] Component (G) is an organic solvent. Illustrative, non-limiting,examples include butyl acetate, amyl acetate, cyclohexyl acetate,3-methoxybutyl acetate, methyl ethyl ketone, methyl amyl ketone,cyclohexanone, cyclopentanone, 3-ethoxyethyl propionate, 3-ethoxymethylpropionate, 3-methoxymethyl propionate, methyl acetoacetate, ethylacetoacetate, diacetone alcohol, methyl pyruvate, ethyl pyruvate,propylene glycol monomethyl ether, propylene glycol monoethyl ether,propylene glycol monomethyl ether propionate, propylene glycol monoethylether propionate, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, 3-methyl-3-methoxybutanol, N-methyl-pyrrolidone,dimethylsulfoxide, γ-butyrolactone, propylene glycol methyl etheracetate, propylene glycol ethyl ether acetate, propylene glycol propylether acetate, methyl lactate, ethyl lactate, propyl lactate, andtetramethylene sulfone. Of these, the propylene glycol alkyl etheracetates and alkyl lactates are especially preferred.

[0082] It is noted that the alkyl groups of the propylene glycol alkylether acetates are preferably those of 1 to 4 carbon atoms, for example,methyl, ethyl and propyl, with methyl and ethyl being especiallypreferred. Since the propylene glycol alkyl ether acetates include 1,2-and 1,3-substituted ones, each includes three isomers depending on thecombination of substituted positions, which may be used alone or inadmixture. It is also noted that the alkyl groups of the alkyl lactatesare preferably those of 1 to 4 carbon atoms, for example, methyl, ethyland propyl, with methyl and ethyl being especially preferred. Thesesolvents may be used alone or in admixture. An exemplary useful solventmixture is a mixture of a propylene glycol alkyl ether acetate and analkyl lactate. The mixing ratio of the propylene glycol alkyl etheracetate and the alkyl lactate is not critical although it is preferredto mix 50 to 99 parts by weight of the propylene glycol alkyl etheracetate with 50 to 1 parts by weight of the alkyl lactate. It is morepreferred to mix 60 to 95% by weight of the propylene glycol alkyl etheracetate with 40 to 5% by weight of the alkyl lactate. A lower proportionof the propylene glycol alkyl ether acetate would invite a problem ofinefficient coating whereas a higher proportion thereof would provideinsufficient dissolution and allow for particle and foreign matterformation. A lower proportion of the alkyl lactate would provideinsufficient dissolution and cause the problem of many particles andforeign matter whereas a higher proportion thereof would lead to acomposition which has a too high viscosity to apply and loses storagestability. The solvent mixture of the propylene glycol alkyl etheracetate and the alkyl lactate may further contain one or more othersolvents.

[0083] Component (A)

[0084] Component (A) is a resin which changes its solubility in analkaline developer solution under the action of an acid. It ispreferably, though not limited thereto, an alkali-soluble resin havingphenolic hydroxyl and/or carboxyl groups in which some or all of thephenolic hydroxyl and/or carboxyl groups are protected with acid-labileprotective groups represented by C—O—C or C—O—Si linkages.

[0085] The alkali-soluble resins having phenolic hydroxyl and/orcarboxyl groups include homopolymers and copolymers of p-hydroxystyrene,m-hydroxystyrene, α-methyl-p-hydroxystyrene, 4-hydroxy-2-methylstyrene,4-hydroxy-3-methylstyrene, methacrylic acid and acrylic acid, and suchcopolymers having a carboxylic derivative or diphenyl ethyleneintroduced at their terminus.

[0086] Also included are copolymers in which units free ofalkali-soluble sites such as styrene, a-methylstyrene, acrylate,methacrylate, hydrogenated hydroxystyrene, maleic anhydride andmaleimide are introduced in addition to the above-described units insuch a proportion that the solubility in an alkaline developer may notbe extremely reduced. Substituents on the acrylates and methacrylatesmay be any of the substituents which do not undergo acidolysis.Exemplary substituents are straight, branched or cyclic C₁₋₈ alkylgroups and aromatic groups such as aryl groups, but not limited thereto.

[0087] Examples of the alkali-soluble resins are given below. Thesepolymers may also be used as the material from which the resin (A) whichchanges its solubility in an alkaline developer under the action of anacid is prepared and as the alkali-soluble resin which serves ascomponent (H) to be described later. Examples includepoly(p-hydroxystyrene), poly(m-hydroxystyrene),poly(4-hydroxy-2-methylstyrene), poly(4-hydroxy-3-methylstyrene),poly(α-methyl-p-hydroxystyrene), partially hydrogenated p-hydroxystyrenecopolymers, p-hydroxystyrene-α-methyl-p-hydroxystyrene copolymers,p-hydroxystyrene-α-methylstyrene copolymers, p-hydroxystyrene-styrenecopolymers, p-hydroxystyrene-m-hydroxystyrene copolymers,p-hydroxystyrene-styrene copolymers, p-hydroxystyrene-acrylic acidcopolymers, p-hydroxystyrene-methacrylic acid copolymers,p-hydroxystyrene-methyl methacrylate copolymers,p-hydroxystyrene-acrylic acid-methyl methacrylate copolymers,p-hydroxystyrene-methyl acrylate copolymers,p-hydroxy-styrene-methacrylic acid-methyl methacrylate copolymers,poly(methacrylic acid), poly(acrylic acid), acrylic acid-methyl acrylatecopolymers, methacrylic acid-methyl methacrylate copolymers, acrylicacid-maleimide copolymers, methacrylic acid-maleimide copolymers,p-hydroxystyrene-acrylic acid-maleimide copolymers, andp-hydroxystyrene-methacrylic acid-maleimide copolymers as well asdendritic and hyperbranched polymers thereof, but are not limited tothese combinations.

[0088] Preferred are poly(p-hydroxystyrene), partially hydrogenatedp-hydroxystyrene copolymers, p-hydroxystyrene-styrene copolymers,p-hydroxystyrene-acrylic acid copolymers, andp-hydroxystyrene-methacrylic acid copolymers as well as dendritic andhyperbranched polymers thereof.

[0089] Alkali-soluble resins comprising units of the following formula(2), (2′) or (2″) are especially preferred.

[0090] Herein R⁴ is hydrogen or methyl, and R⁵ is a straight, branchedor cyclic alkyl group of 1 to 8 carbon atoms. Subscript x is 0 or apositive integer, and y is a positive integer, satisfying x+y≦5.Subscripts M and N are positive integers, satisfying 0<N/(M+N)≦0.5. ZZis a divalent organic group selected from among CH₂, CH(OH), CR⁵(OH),C═O and C(OR⁵)(OH) or a trivalent organic group represented by —C(OH)═.Subscript E, which may be identical or different, is a positive integer,and K is a positive integer, satisfying 0.001≦K/(K+E)≦0.1, and XX is 1or 2.

[0091] The alkali-soluble resins or polymers should preferably have aweight average molecular weight (Mw) of 3,000 to 100,000. Many polymerswith Mw of less than 3,000do not perform well and are poor in heatresistance and film formation. Many polymers with Mw of more than100,000 give rise to a problem with respect to dissolution in the resistsolvent and developer. The polymer should also preferably have adispersity (Mw/Mn) of up to 3.5, and more preferably up to 1.5. With adispersity of more than 3.5, resolution is low in many cases. Althoughthe preparation method is not critical, a poly(p-hydroxystyrene) orsimilar polymer with a low dispersity or narrow dispersion can besynthesized by living anion polymerization.

[0092] The dendritic or hyperbranched polymer of phenol derivativerepresented by formula (2″) can be synthesized by effecting living anionpolymerization of a polymerizable monomer such as 4-tert-butoxystyreneand reacting a branching monomer such as chloromethylstyrene asappropriate during the living anion polymerization.

[0093] More particularly, living anion polymerization is started using apolymerizable monomer such as 4-tert-butoxystyrene. After apredetermined amount has been polymerized, a branching monomer such aschloromethylstyrene is introduced and reacted with the intermediate.Then the polymerizable monomer such as 4-tert-butoxystyrene and/or thebranching monomer such as chloromethylstyrene is added again forpolymerization. This operation is repeated many times until a desireddendritic or hyperbranched polymer is obtained. If necessary, theprotective groups used to enable living polymerization are deblocked,yielding a dendritic or hyperbranched polymer of phenol derivative.

[0094] Examples of the branching monomer are given below.

[0095] R⁴, R⁵, x and y are as defined above.

[0096] Illustrative examples of the dendritic or hyperbranched polymerare those having recurring units of the following approximate formulas(8) to (12).

[0097] Herein, broken lines represent polymer chains of the phenolderivative monomer, and D represents units based on the branchingmonomer. The number of broken line segments between D and D is depictedmerely for the sake of convenience, independent of the number ofrecurring units in the polymer chain included between D and D.

[0098] The dendritic or hyperbranched polymer of a phenol derivative isprepared by effecting living polymerization of the phenol derivative,reacting with a compound having a polymerizable moiety and a terminatingmoiety and proceeding further polymerization. By repeating thisoperation desired times, a dendritic or hyperbranched polymer of phenolderivative can be synthesized. The living polymerization may be effectedby any desired technique although living anion polymerization ispreferred because of ease of control.

[0099] For living anion polymerization to take place, the reactionsolvent is preferably selected from toluene, benzene, tetrahydrofuran,dioxane, and diethyl ether. Of these, polar solvents such astetrahydrofuran, dioxane, and diethyl ether are preferable. They may beused alone or in admixture of two or more.

[0100] The initiator used herein is preferably selected from sec-butyllithium, n-butyl lithium, naphthalene sodium and cumyl potassium. Theamount of the initiator used is proportional to the design molecularweight.

[0101] Preferred reaction conditions include a temperature of −80° C. to100° C., preferably −70° C. to 0° C., and a time of about 0.1 to 50hours, preferably about 0.5 to 5 hours.

[0102] One exemplary reaction scheme using sec-butyl lithium as theinitiator and 4-chloromethylstyrene as the branching monomer is shownbelow. The branching coefficient can be altered by repeating thereaction step any desired times.

[0103] Herein, R⁴, R⁵, x and y are as defined above, m₁ and m₂ each are0 or a positive integer, and RR is a substituent capable of withstandingliving anion polymerization.

[0104] The living polymer thus obtained is deactivated or stopped, andthe substituent RR which has been introduced for the progress of livinganion polymerization is deblocked, obtaining an alkali-soluble resin.

[0105] The resin (A) is an alkali-soluble resin (as mentioned above)having hydroxyl or carboxyl groups, some of which are replaced by acidlabile groups such that the solubility in an alkaline developer changesas a result of severing of the acid labile groups under the action of anacid generated by the photoacid generator upon exposure to radiation.Especially preferred is a polymer comprising recurring units of theabove formula (2) or (2″) and containing phenolic hydroxyl groups inwhich hydrogen atoms of the phenolic hydroxyl group are replaced by acidlabile groups of one or more types in a proportion of more than 0 moltto 80 mol % on the average of the entire hydrogen atoms of the phenolichydroxyl group, the polymer having a weight average molecular weight of3,000 to 100,000.

[0106] Also preferred is a polymer comprising recurring units of theabove formula (2′), that is, a copolymer comprising p-hydroxystyreneand/or α-methyl-p-hydroxystyrene and acrylic acid and/or methacrylicacid, wherein some of the hydrogen atoms of carboxyl groups of theacrylic acid and/or methacrylic acid are replaced by acid labile groupsof one or more types to form an ester, the units based on the acrylicester and/or methacrylic ester are contained in a proportion of morethan 0 molt to 50 mol %, on the average, of the copolymer, and whereinsome of the hydrogen atoms of the phenolic hydroxyl groups ofp-hydroxystyrene and/or α-methyl-p-hydroxystyrene may be replaced byacid labile groups of one or more types. Further preferred is such acopolymer in which the units based on the acrylic ester and/ormethacrylic ester and the p-hydroxystyrene and/orα-methyl-p-hydroxystyrene having acid labile groups substituted thereonare contained in a proportion of more than 0 mol % to 80 mol %, on theaverage, of the copolymer.

[0107] Exemplary such polymers are polymers comprising recurring unitsrepresented by the following general formula (2a), (2a′) or (2a″) andhaving a weight average molecular weight of 3,000 to 100,000.

[0108] Herein, R⁴ is hydrogen or methyl. R⁵ is a straight, branched orcyclic alkyl group of 1 to 8 carbon atoms. R⁶ is an acid labile group.R⁶a is hydrogen or an acid labile group, at least some, preferably allof the R^(6a) groups are substituents of formula (1) and/or acid labilegroups. Letter x is 0 or a positive integer, and y is a positiveinteger, satisfying x+y≦5. The R⁶ groups may be the same or differentwhen y is 2 or more. S and T are positive integers, satisfying0.01≦S/(S+T)≦0.4. M and N are positive integers, L is 0 or a positiveinteger, satisfying 0<N/(M+N)≦0.4 and 0.01≦(N+L)/(M+N+L)≦0.4. ZZ is adivalent organic group selected from among CH₂, CH(OH), CR⁵(OH), C═O andC(OR⁵)(OH) or a trivalent organic group represented by —C(OH)═.Subscript E, which may be identical or different, is a positive integer,and K is a positive integer, satisfying 0.001≦K/(K+S+T)≦0.1, and XX is 1or 2.

[0109] R⁵ stands for straight, branched or cyclic C₁₋₈ alkyl groups, forexample, methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl,tert-butyl, cyclohexyl and cyclopentyl.

[0110] The acid labile groups are selected from a variety of suchgroups. The preferred acid labile groups are groups of the followinggeneral formulae (4) to (7), tertiary alkyl group of 4 to 20 carbonatoms, preferably 4 to 15 carbon atoms, trialkylsilyl groups whose alkylgroups each have 1 to 6 carbon atoms, oxoalkyl groups of 4 to 20 carbonatoms, or aryl-substituted alkyl groups of 7 to 20 carbon atoms.

[0111] Herein R¹⁰ and R¹¹ are independently hydrogen or straight,branched or cyclic alkyl groups of 1 to 18 carbon atoms, preferably 1 to10 carbon atoms, for example, methyl, ethyl, propyl, isopropyl, n-butyl,sec-butyl, tert-butyl, cyclopentyl, cyclohexyl, 2-ethylhexyl andn-octyl. R¹² is a monovalent hydrocarbon group of 1 to 18 carbon atoms,preferably 1 to 10 carbon atoms, which may have a hetero atom (e.g.,oxygen atom), for example, straight, branched or cyclic alkyl groups,and such groups in which some hydrogen atoms are replaced by hydroxyl,alkoxy, oxo, amino or alkylamino groups. Illustrative examples of thesubstituted alkyl groups are given below.

[0112] A pair of R¹⁰ and R¹¹, a pair of R¹⁰ and R¹², or a pair of R¹¹and R¹², taken together, may form a ring. Each of R¹⁰, R¹¹ and R¹² is astraight or branched alkylene group of 1 to 18 carbon atoms, preferably1 to 10 carbon atoms, when they form a ring.

[0113] R¹³ is a tertiary alkyl group of 4 to 20 carbon atoms, preferably4 to 15 carbon atoms, a trialkylsilyl group whose alkyl groups each have1 to 6 carbon atoms, an oxoalkyl group of 4 to 20 carbon atoms or agroup of formula (4). Exemplary tertiary alkyl groups are tert-butyl,tert-amyl, 1,1-diethylpropyl, 1-methylcyclopentyl, 1-ethylcyclopentyl,1-isopropylcyclopentyl, 1-butylcyclopentyl, 1-methylcyclohexyl,1-ethylcyclohexyl, 1-isopropylcyclohexyl, 1-butyl-cyclohexyl,1-ethyl-2-cyclopentenyl, 1-ethyl-2-cyclohexenyl, and2-methyl-2-adamantyl. Exemplary trialkylsilyl groups are trimethylsilyl,triethylsilyl, and dimethyl-tert-butylsilyl. Exemplary oxoalkyl groupsare 3-oxocyclohexyl, 4-methyl-2-oxooxan-4-yl, and5-methyl-5-oxooxolan-4-yl. Letter z is an integer of 0 to 6.

[0114] R¹⁴ is a straight, branched or cyclic alkyl group of 1 to 8carbon atoms or substituted or unsubstituted aryl group of 6 to 20carbon atoms. Exemplary straight, branched or cyclic alkyl groupsinclude methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl,tert-butyl, tert-amyl, n-pentyl, n-hexyl, cyclopentyl, cyclohexyl,cyclopentylmethyl, cyclopentylethyl, cyclohexylmethyl andcyclohexylethyl. Exemplary substituted or unsubstituted aryl groupsinclude phenyl, methylphenyl, naphthyl, anthryl, phenanthryl, andpyrenyl. Letter h′ is equal to 0 or 1, i is equal to 0, 1, 2 or 3,satisfying 2h′+i=2 or 3.

[0115] R¹⁵ is a straight, branched or cyclic alkyl group of 1 to 8carbon atoms or substituted or unsubstituted aryl group of 6 to 20carbon atoms, examples of which are as exemplified for R¹⁴. R¹⁶ to R²⁵are independently hydrogen or monovalent hydrocarbon groups of 1 to 15carbon atoms which may contain a hetero atom, for example, straight,branched or cyclic alkyl groups such as methyl, ethyl, propyl,isopropyl, n-butyl, sec-butyl, tert-butyl, tert-amyl, n-pentyl, n-hexyl,n-octyl, n-nonyl, n-decyl, cyclopentyl, cyclohexyl, cyclopentylmethyl,cyclopentylethyl, cyclopentylbutyl, cyclohexylmethyl, cyclohexylethyl,and cyclohexylbutyl, and substituted ones of these groups in which somehydrogen atoms are replaced by hydroxyl, alkoxy, carboxy,alkoxycarbonyl, oxo, amino, alkylamino, cyano, mercapto, alkylthio, andsulfo groups. R¹⁶ to R²⁵, for example, a pair of R¹⁶ and R¹⁷, a pair ofR¹⁶ and R¹⁸, a pair of R¹⁷ and R¹⁹, a pair of R¹⁸ and R¹⁹, a pair of R²⁰and R²¹, or a pair of R²² and R²³, taken together, may form a ring. WhenR¹⁶ to R²⁵ form a ring, they are divalent C₁₋₁₅ hydrocarbon groups whichmay contain a hetero atom, examples of which are the above-exemplifiedmonovalent hydrocarbon groups with one hydrogen atom eliminated. Also,two of R¹⁶ to R²⁵ which are attached to adjacent carbon atoms (forexample, a pair of R¹⁶ and R¹8, a pair of R¹⁸ and R²⁴, or a pair of R²²and R²⁴) may directly bond together to form a double bond.

[0116] Of the acid labile groups of formula (4), illustrative examplesof the straight or branched groups are given below.

[0117] Of the acid labile groups of formula (4), illustrative examplesof the cyclic groups include tetrahydrofuran-2-yl,2-methyltetrahydrofuran-2-yl, tetrahydropyran-2-yl and2-methyltetrahydropyran-2-yl.

[0118] Illustrative examples of the acid labile groups of formula (5)include tert-butoxycarbonyl, tert-butoxycarbonylmethyl,tert-amyloxycarbonyl, tert-amyloxycarbonylmethyl,1,1-diethylpropyloxycarbonyl, 1,1-diethylpropyloxycarbonylmethyl,1-ethylcyclopentyloxycarbonyl, 1-ethylcyclopentyloxycarbonylmethyl,1-ethyl-2-cyclopentenyloxycarbonyl,1-ethyl-2-cyclopentenyloxycarbonylmethyl, 1-ethoxyethoxycarbonylmethyl,2-tetrahydropyranyloxycarbonylmethyl, and2-tetrahydrofuranyloxycarbonylmethyl.

[0119] Illustrative examples of the acid labile groups of formula (6)include 1-methylcyclopentyl, 1-ethylcyclopentyl, 1-n-propylcyclopentyl,1-isopropylcyclopentyl, 1-n-butyl-cyclopentyl, 1-sec-butylcyclopentyl,1-methylcyclohexyl, 1-ethylcyclohexyl, 3-methyl-1-cyclopenten-3-yl,3-ethyl-1-cyclopenten-3-yl, 3-methyl-1-cyclohexen-3-yl, and3-ethyl-1-cyclohexen-3-yl.

[0120] Illustrative examples of the acid labile groups of formula (7)are given below.

[0121] Exemplary of the tertiary alkyl group of 4 to 20 carbon atoms,preferably 4 to 15 carbon atoms, are tert-butyl, tert-amyl,3-ethyl-3-pentyl and dimethylbenzyl.

[0122] Exemplary of the trialkylsilyl groups whose alkyl groups eachhave 1 to 6 carbon atoms are trimethylsilyl, triethylsilyl, andtert-butyldimethylsilyl.

[0123] Exemplary of the oxoalkyl groups of 4 to 20 carbon atoms are3-oxocyclohexyl and groups represented by the following formulae.

[0124] Exemplary of the aryl-substituted alkyl groups of 7 to 20 carbonatoms are benzyl, methylbenzyl, dimethylbenzyl, diphenylmethyl, and1,1-diphenylethyl.

[0125] In the resist composition comprising an onium salt of formula(1), (1a), (1a′) or (1b), the resin (A) may be the polymer of formula(2) or (21) in which some of the hydrogen atoms of the phenolic hydroxylgroups and/or all of the carboxyl groups are partially replaced by acidlabile groups of one or more types, and the hydrogen atoms of theremaining phenolic hydroxyl groups are crosslinked within a moleculeand/or between molecules, in a proportion of more than 0 mol % to 50 mol%, on the average, of the entire phenolic hydroxyl groups on thepolymer, with crosslinking groups having C—O—C linkages represented bythe following general formula (3a) or (3b).

[0126] The crosslinking groups having C—O—C linkages include groupsrepresented by the following general formula (3a) or (3b).

[0127] Herein, each of R⁷ and R⁸ is hydrogen or a straight, branched orcyclic alkyl group of 1 to 8 carbon atoms, or R⁷ and R⁸, taken together,may form a ring, and each of R⁷ and R⁸ is a straight or branchedalkylene group of 1 to 8 carbon atoms when they form a ring. R⁹ is astraight, branched or cyclic alkylene group of 1 to 10 carbon atoms,letter b is 0 or an integer of 1 to 10. Letter a′ is an integer of 1 to7 and preferably 1 to 3, and b is 0 or an integer of 1 to 10 andpreferably 0 or an integer of 1 to 5. A is an (a′+1)-valent aliphatic oralicyclic saturated hydrocarbon group, aromatic hydrocarbon group orheterocyclic group of 1 to 50 carbon atoms, which may be separated by ahetero atom and in which some of the hydrogen atoms attached to carbonatoms may be replaced by hydroxyl, carboxyl, carbonyl or halogen.

[0128] B is —CO—O—, —NHCO—O— or —NHCONH—. Examples of the straight,branched or cyclic C₁₋₈ alkyl group represented by R⁷ and R⁸ are asexemplified for R⁵.

[0129] Examples of the straight, branched or cyclic C₁₋₁₀ alkylene grouprepresented by R⁹ include methylene, ethylene, propylene, isopropylene,n-butylene, isobutylene, cyclohexylene, and cyclopentylene.

[0130] Exemplary halogen atoms are fluorine, chlorine, bromine andiodine.

[0131] Illustrative examples of A are described later. Thesecrosslinking groups of formulae (3a) and (3b) originate from alkenylether compounds and halogenated alkyl ether compounds to be describedlater.

[0132] As understood from the value of a′ in formula (3a) or (3b), thecrosslinking group having C—O—C linkages is not limited to a divalentone and trivalent to octavalent groups are acceptable. The detail of thecrosslinking group is described in JP-A 2000-194127, which isincorporated herein by reference. Some preferred examples are givenbelow.

[0133] In the resist composition of the invention, the preferred polymeris a polymer comprising recurring units of the following general formula(2b), (2b′) or (2b″), and more preferably the same polymer in whichhydrogen atoms of phenolic hydroxyl groups represented by R areeliminated to leave oxygen atoms which are crosslinked within a moleculeand/or between molecules with crosslinking groups having C—O—C linkagesrepresented by the above formula (3a) or (3b).

[0134] Herein, R represents a hydroxyl group or an acid labile grouphaving an oxygen atom attached thereto (i.e., —O-acid labile group)other than —OCR¹⁰R¹¹OR¹² and —O(CH₂)_(z)COOR¹³ R⁴ is hydrogen or methyl,R⁵ is a straight, branched or cyclic alkyl group of 1 to 8 carbon atoms.R¹⁰ and R¹¹ are independently hydrogen or straight, branched or cyclicalkyl groups of 1 to 18 carbon atoms, R¹² is a monovalent hydrocarbongroup of 1 to 18 carbon atoms which may have a hetero atom, or a pair ofR¹⁰ and R¹¹, R¹⁰ and R¹², or R¹¹ and R¹², taken together, may form aring, with the proviso that each of R¹⁰, R¹¹ and R¹² is a straight orbranched alkylene group of 1 to 18 carbon atoms when they form a ring.R¹³ is a tertiary alkyl group of 4 to 20 carbon atoms, anaryl-substituted alkyl group of 7 to 20 carbon atoms, an oxoalkyl groupof 4 to 20 carbon atoms or a group represented by —CR¹⁰R¹¹OR¹². Letter zis an integer of 0 to 6. S2 is a positive number, each of S1, T1, and T2is 0 or a positive number, satisfying 0<S1/(S1+T1+T2+S2)≦0.8,0≦T1/(S1+T1+T2+S2)≦0.8, 0≦T2/(S1+T1+T2+S2)≦0.8, and S1+T1+T2+S2=1. T1and T2 are not equal to 0 at the same time. Each of u and w is 0 or apositive integer, and v is a positive integer, satisfying u+v+w≦5.Letters x and y are as defined above.

[0135] More preferably, S1, S2, T1 and T2 satisfy the following ranges.

[0136] 0≦S1/(S1+T1+T2+S2)≦0.5,

[0137] especially 0.002≦Si/(S1+T1+T2+S2)≦0.2

[0138] 0<T1/(S1+T1+T2+S2)≦0.5,

[0139] especially 0≦T1/(S1+T1+T2+S2)≦0.4

[0140] 0≦T2/(S1+T1+T2+S2)≦0.5,

[0141] especially 0≦T2/(S1+T1+T2+S2)≦0.4

[0142] 0.4≦S2/(S1+T1+T2+S2)≦1,

[0143] especially 0.5≦S2/(S1+T1+T2+S2)≦0.9

[0144] 0≦(T1+T2)/(S1+T1+T2+S2)≦0.5,

[0145] especially 0.1≦(T1+T2)/(S1+T1+T2+S2)≦0.4

[0146] It is also preferred that T1/(T1+T2) be from 0 to 1, morepreferably from 0.5 to 1, and most preferably from 0.7 to 1.

[0147] Herein, R, R⁴, R⁵, R¹⁰, R¹¹, R¹², R¹³, x, y, z, u, v and w are asdefined above. R^(6a) is hydrogen or an acid labile group as mentionedabove, and at least some, preferably all of the R^(6a) groups are acidlabile groups. M2 is a positive number, each of M1, L1, L2 and N is 0 ora positive number, satisfying 0≦M1/(M1+L1+L2+N+M2)≦0.8,0≦L1/(M1+L1+L2+N+M2)≦0.8, 0≦L2/(M1+L1+L2+N+M2)≦0.8,0≦N/(M1+L1+L2+N+M2)≦0.8, and M1+L1+L2+N+M2=1. L1, L2 and N are not equalto 0 at the same time.

[0148] More preferably, M1, L1, L2, N and M2 satisfy the followingranges.

[0149] 0≦M1/(M1+L1+L2+N+M2)≦0.5,

[0150] especially 0.002≦Ml/(M1+L1+L2+N+M2)≦0.2

[0151] 0≦L1/(M1+L1+L2+N+M2)≦0.5,

[0152] especially 0≦L1/(M1+L1+L2+N+M2)≦0.4

[0153] 0≦L2/(M1+L1+L2+N+M2)≦0.5,

[0154] especially 0≦L2/(M1+L1+L2+N+M2)≦0.4

[0155] 0≦N/(M1+L1+L2+N+M2)≦0.5,

[0156] especially 0≦N/(M1+L1+L2+N+M2)≦0.4

[0157] 0.4≦M2/(M1+L1+L2+N+M2)≦1,

[0158] especially 0.5≦M2/(M1+L1+L2+N+M2)≦0.9

[0159] 0≦(L1+L2+N)/(M1+L1+L2+N+M2)≦0.5,

[0160] especially 0.1≦(L1+L2+N)/(M1+L1+L2+N+M2)≦0.4

[0161] It is also preferred that N/(L1+L2+N) be from 0 to 1, morepreferably from 0.5 to 1, and most preferably from 0.7 to 1.

[0162] Herein, R, R⁴, R⁵, R¹⁰, R¹¹, R¹², R¹³, S1, S2, T1, T2, u, w, v,n, x, y, and z are as defined above. ZZ is a divalent organic groupselected from among CH₂, CH(OH), CR⁵(OH), C═O and C(OR⁵)(OH) or atrivalent organic group represented by —C(OH)═. Subscript XX is 1 or 2,and K is a positive integer, satisfying 0.001≦K/(S1+T1+T2+S2+K)≦0.1.

[0163] In this polymer as well, the total amount of the acid labilegroups and crosslinking groups is, on the average, more than 0 mol % to80 mol % and especially 2 to 50 mol %, based on the entire phenolichydroxyl groups in formula (2b) or (2b″) or the phenolic hydroxyl groupsand carboxyl groups in formula (2b′) combined.

[0164] An appropriate proportion of crosslinking groups having C—O—Clinkages is, on the average, from more than 0 mol % to 50 mol %, andespecially from 0.2 to 20 mol %. With 0 mol %, few benefits of thecrosslinking group are obtained, resulting in a reduced contrast ofalkali dissolution rate and a low resolution. With more than 50 mol %, atoo much crosslinked polymer would gel, become insoluble in alkali,induce a film thickness change, internal stresses or bubbles upon alkalidevelopment, and lose adhesion to the substrate due to less hydrophilicgroups.

[0165] The proportion of acid labile groups is on the average preferablyfrom more than 0 mol % to 80 mol %, especially from 10 to 50 mol %. With0 mol %, there may result a reduced contrast of alkali dissolution rateand low resolution. With more than 80 mol %, there may result a loss ofalkali dissolution, less affinity to an alkali developer upondevelopment, and a low resolution.

[0166] By properly selecting the proportions of crosslinking groupshaving C—O—C linkages and acid labile groups within the above-definedranges, it becomes possible to control the size and configuration of aresist pattern as desired. In the resist composition comprising theonium salt according to the invention, the contents of crosslinkinggroups having C—O—C linkages and acid labile groups in the polymer havesubstantial influence on the dissolution rate contrast of a resist filmand govern the properties of the resist composition relating to the sizeand configuration of a resist pattern.

[0167] Now “A” in the crosslinking group is described. The (a′+1)-valentorganic groups represented by A include hydrocarbon groups, for example,substituted or unsubstituted alkylene groups preferably having 1 to 50carbon atoms, and especially 1 to 40 carbon atoms, substituted orunsubstituted arylene groups preferably having 6 to 50 carbon atoms, andespecially 6 to 40 carbon atoms (these alkylene and arylene groups mayhave an intervening hetero atom or group such as O, NH, N(CH₃), S orSO₂, and where substituted, the substituents are hydroxyl, carboxyl,acyl and fluorine), and combinations of these alkylene groups with thesearylene groups. Additional examples include (a′+1)-valent heterocyclicgroups, and combinations of these heterocyclic groups with the foregoinghydrocarbon groups.

[0168] Illustrative examples of A are described in JP-A 2000-194127.Preferred are those of formula (3a) wherein R¹¹ is methyl, R¹² ishydrogen, a′ is 1, b is 0, and A is ethylene, 1,4-butylene or1,4-cyclohexylene.

[0169] In preparing the polymer which is crosslinked within a molecularand/or between molecules with crosslinking groups having C-O-C linkages,synthesis may be made by reacting a corresponding non-crosslinkedpolymer with an alkenyl ether in the presence of an acid catalyst in aconventional manner.

[0170] Alternatively, where decomposition of other acid labile groupstakes place in the presence of an acid catalyst, the end product can besynthesized by first reacting an alkenyl ether with hydrochloric acid orthe like to form a halogenated alkyl ether, and reacting it with apolymer under basic conditions in a conventional manner.

[0171] Illustrative examples of the alkenyl ether are described in JP-A2000-194127. Preferred among these are ethylene glycol divinyl ether,1,2-propanediol divinyl ether, 1,3-propanediol divinyl ether,1,3-butanediol divinyl ether, 1,4-butanediol divinyl ether, and1,4-cyclohexanediol divinyl ether.

[0172] In the resist composition comprising the onium salt according tothe invention, the resin used as component (A) is as described abovewhile the preferred acid labile groups introduced therein are1-ethylcyclohexyl, 1-ethylcyclopentyl, 1-ethylcyclohexylcarbonylmethyl,tert-amyl, 1-ethoxyethyl, 1-ethoxypropyl, tetrahydrofuranyl,tetrahydropyranyl, tert-butyl, tert-butoxycarbonyl,tert-butoxycarbonylmethyl groups, and substituents of formula (3a)wherein R⁷ is methyl, R⁸ is hydrogen, a′ is 1, b is 0, and A isethylene, 1,4-butylene or 1,4-cyclohexylene.

[0173] In a single polymer, these substituents may be incorporated aloneor in admixture of two or more types. A blend of two or more polymershaving substituents of different types is also acceptable.

[0174] Appropriate combinations of substituents of two or more typesinclude a combination of acetal with acetal analog, a combination ofacetal with a substituent having a different degree of scission by acidsuch as tert-butoxy, a combination of a crosslinking acid labile groupwith acetal, and a combination of a crosslinking acid labile group witha substituent having a different degree of scission by acid such astert-butoxy.

[0175] The percent proportion of these substituents substituting forphenol and carboxyl groups in the polymer is not critical. Preferablythe percent substitution is selected such that when a resist compositioncomprising the polymer is applied onto a substrate to form a coating,the unexposed area of the coating may have a dissolution rate of 0.01 to10 Å/sec in a 2.38% tetramethylammonium hydroxide (TMAH) developer.

[0176] On use of a polymer containing a greater proportion of carboxylgroups which can reduce the alkali dissolution rate, the percentsubstitution must be increased or non-acid-labile substituents to bedescribed later must be introduced.

[0177] When acid labile groups for intramolecular and/or intermolecularcrosslinking are to be introduced, the percent proportion ofcrosslinking substituents is preferably up to 20%, more preferably up to10%. If the percent substitution of crosslinking substituents is toohigh, crosslinking results in a higher molecular weight which canadversely affect dissolution, stability and resolution. It is alsopreferred to further introduce another non-crosslinking acid labilegroup into the crosslinked polymer at a percent substitution of up to10% for adjusting the dissolution rate to fall within the above range.

[0178] In the case of poly(p-hydroxystyrene), the optimum percentsubstitution differs between a substituent having a strong dissolutioninhibitory action such as a tert-butoxycarbonyl group and a substituenthaving a weak dissolution inhibitory action such as an acetal groupalthough the overall percent substitution is preferably 10 to 40%, morepreferably 20 to 30%.

[0179] Polymers having such acid labile groups introduced therein shouldpreferably have a weight average molecular weight (Mw) of 3,000 to100,000. With a Mw of less than 3,000, polymers would perform poorly andoften lack heat resistance and film formability. Polymers with a Mw ofmore than 100,000 would be less soluble in a developer and a resistsolvent.

[0180] Where non-crosslinking acid labile groups are introduced, thepolymer should preferably have a dispersity (Mw/Mn) of up to 3.5,preferably up to 1.5. A polymer with a dispersity of more than 3.5 oftenresults in a low resolution. Where crosslinking acid labile groups areintroduced, the starting alkali-soluble resin should preferably have adispersity (Mw/Mn) of up to 1.5, and the dispersity is kept at 3 orlower even after protection with crosslinking acid labile groups. If thedispersity is higher than 3, dissolution, coating, storage stabilityand/or resolution is often poor.

[0181] To impart a certain function, suitable substituent groups may beintroduced into some of the phenolic hydroxyl and carboxyl groups on theacid labile group-protected polymer. Exemplary are substituent groupsfor improving adhesion to the substrate, non-acid-labile groups foradjusting dissolution in an alkali developer, and substituent groups forimproving etching resistance. Illustrative, non-limiting, substituentgroups include 2-hydroxyethyl, 2-hydroxypropyl, methoxymethyl,methoxycarbonyl, ethoxycarbonyl, methoxycarbonylmethyl,ethoxy-carbonylmethyl, 4-methyl-2-oxo-4-oxolanyl,4-methyl-2-oxo-4-oxanyl, methyl, ethyl, propyl, n-butyl, sec-butyl,acetyl, pivaloyl, adamantyl, isobornyl, and cyclohexyl.

[0182] Illustrative examples of the onium salts of formulae (1), (1a),(1a′) and (1b) as the photoacid generator (B) are as described above,and combinations of cations with anions are listed below again.

[0183] Examples of the sulfonate anion include4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate, 5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate, 6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-(phenylsulfonyloxy)naphthalene-1-sulfonate,8-(phenylsulfonyloxy)naphthalene-1-sulfonate, 5-(phenylsulfonyloxy)naphthalene-1sulfonate,6-(phenylsulfonyloxy)naphthalene-2-sulfonate,4-(2-naphthylsulfonyloxy)naphthalene-1-sulfonate,8-(2-naphthylsulfonyloxy)naphthalene-1-sulfonate,5-(2-naphthylsulfonyloxy)naphthalene-1-sulfonate,6-(2-naphthylsulfonyloxy)naphthalene-2-sulfonate,6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,6,7-bis(phenylsulfonyloxy)naphthalene-2-sulfonate,5,7-dinitro-8-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate, and5,7-dinitro-8-(phenylsulfonyloxy)naphthalene-2-sulfonate.

[0184] Exemplary iodonium cations include diphenyliodonium,bis(4-tert-butylphenyl)iodonium, 4-methoxyphenylphenyliodonium,4-ethoxyphenylphenyliodonium, and 4-tert-butoxyphenylphenyliodonium,with the diphenyliodonium and bis(4-tert-butylphenyl)iodonium arepreferred.

[0185] Exemplary sulfonium cations include triphenylsulfonium,4-hydroxyphenyldiphenylsulfonium, (4-methylphenyl)diphenylsulfonium,bis(4-methylphenyl)phenylsulfonium, tris(4-methylphenyl)sulfonium,(4-methoxyphenyl)diphenylsulfonium, bis(4-methoxyphenyl)phenylsulfonium,tris(4-methoxyphenyl)sulfonium, (4-tert-butylphenyl)diphenylsulfonium,bis(4-tert-butylphenyl)phenylsulfonium,tris(4-tert-butylphenyl)sulfonium,(4-tertbutoxyphenyl)diphenylsulfonium,bis(4-tert-butoxyphenyl)phenylsulfonium,tris(4-tert-butoxyphenyl)sulfonium,(3-tert-butoxyphenyl)diphenylsulfonium,bis(3-tert-butoxyphenyl)phenylsulfonium,tris(3-tert-butoxyphenyl)sulfonium,(3,4-di-tert-butoxyphenyl)diphenylsulfonium,bis(3,4-di-tert-butoxyphenyl)phenylsulfonium,tris(3,4-di-tert-butoxyphenyl)sulfonium,diphenyl(4-thiophenoxyphenyl)sulfonium,(4-tert-butoxycarbonylmethyloxyphenyl)diphenylsulfonium,tris(4-tert-butoxycarbonylmethyloxyphenyl)sulfonium,(4-tert-butoxyphenyl)bis(4-dimethylaminophenyl)sulfonium,tris(4-dimethylaminophenyl)sulfonium, 2-naphthyldiphenylsulfonium,dimethyl-2-naphthylsulfonium, 4-hydroxyphenyldimethylsulfonium,4-methoxyphenyldimethylsulfonium, dimethylphenylsulfonium,diphenylmethylsulfonium, trimethylsulfonium,2-oxocyclohexylcyclohexylmethylsulfonium,2-oxocyclohexyl-methyl-phenylsulfonium,2-oxocyclopentylmethyl-phenylsulfonium,2-oxocyclopropyl-methyl-phenylsulfonium, and tribenzylsulfonium. Ofthese, triphenylsulfonium, 4-tert-butoxyphenyldiphenylsulfonium,dimethylphenylsulfonium, and 4-tert-butylphenyldiphenylsulfonium arepreferred.

[0186] Especially useful onium salts are: triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,triphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,triphenylsulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-tert-butoxyphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-tert-butoxyphenyldiphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-tert-butoxyphenyldiphenylsulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4′-tert-butoxyphenyldiphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-methylphenyl)sulfonium 4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate, tris(4-methylphenyl)sulfonium8-(4′-methylphenylsulfonyloxy) naphthalene-1-sulfonate,tris(4-methylphenyl)sulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-methylphenyl)sulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-methylphenyldiphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-methylphenyldiphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-methylphenyldiphenylsulfonium5-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate,4-methylphenyldiphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-tert-butylphenyl)sulfonium4-(phenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-tert-butylphenyl)sulfonium8-(phenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-tert-butylphenyl)sulfonium5-(phenylsulfonyloxy)naphthalene-1-sulfonate,tris(4-tert-butylphenyl)sulfonium6-(phenylsulfonyloxy)naphthalene-2-sulfonate, triphenylsulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,4-tert-butoxyphenyldiphenylsulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-methylphenyl)sulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,tris(4-tert-butylphenyl)sulfonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate,bis(4-tert-butylphenyl)iodonium4-(phenylsulfonyloxy)naphthalene-1-sulfonate,bis(4-tert-butylphenyl)iodonium8-(phenylsulfonyloxy)naphthalene-1-sulfonate,bis(4-tert-butylphenyl)iodonium5-(phenylsulfonyloxy)naphthalene-1-sulfonate,bis(4-tert-butylphenyl)iodonium6-(phenylsulfonyloxy)naphthalene-2-sulfonate, andbis(4-tert-butylphenyl)iodonium6,7-bis(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate.

[0187] In the chemical amplification type resist composition, anappropriate amount of the onium salt (B) of formula (1), (1a), (1a′) or(1b) added is from 0.5 part to 20 parts by weight, and preferably from 1to 10 parts by weight, per 100 parts by weight of the solids in thecomposition. The photoacid generators may be used alone or in admixtureof two or more. The transmittance of the resist film can be controlledby using a photoacid generator having a low transmittance at theexposure wavelength and adjusting the amount of the photoacid generatoradded.

[0188] Component (C)

[0189] In one preferred embodiment, the resist composition furthercontains (C) a compound capable of generating an acid upon exposure tohigh energy radiation, that is, a second photoacid generator other thanthe onium salt (B). The second photoacid generators include sulfoniumsalts and iodonium salts as well as sulfonyldiazomethane,N-sulfonyloxyimide, benzoinsulfonate, nitrobenzylsulfonate, sulfone, andglyoxime derivatives. They may be used alone or in admixture of two ormore. Exemplary photoacid generators are described in JP-A 2000-194127,though not limited thereto.

[0190] Preferred photoacid generators used herein are sulfonium saltsand bissulfonyldiazomethanes.

[0191] Sulfonium salts are salts of sulfonium cations with sulfonateanions. In addition to those exemplified in connection with formulae(1), (1a) and (1a′), exemplary sulfonium cations includetriphenylsulfonium, 4-tert-butoxyphenyldiphenylsulfonium,dimethylphenylsulfonium, 4-tert-butylphenyldiphenylsulfonium,tris(4-tert-butylphenyl)sulfonium and tris(4-methylphenyl)sulfonium.Exemplary sulfonate anions include benzenesulfonate, toluenesulfonate,trifluoromethylbenzenesulfonate, pentafluorobenzenesulfonate,2,2,2-trifluoroethanesulfonate, nonafluorobutanesulfonate,heptadecafluorooctanesulfonate, and camphorsulfonate anions.

[0192] Exemplary bissulfonyldiazomethane compounds includebis(tert-butylsulfonyl)diazomethane,bis(cyclohexylsulfonyl)diazomethane, bis(tert-amylsulfonyl)diazomethane,bis(phenylsulfonyl)diazomethane,bis(4-methylphenylsulfonyl)diazomethane,bis(4-tert-butylphenylsulfonyl)diazomethane, andbis(2,4-dimethylphenylsulfonyl)diazomethane.

[0193] While the anion of the optimum acid to be generated differsdepending on the ease of scission of acid labile groups introduced inthe polymer, an anion which is non-volatile and not extremely diffusiveis generally chosen. The preferred anions include benzenesulfonic acidanions, toluenesulfonic acid anions, pentafluorobenzenesulfonic acidanions, 2,2,2-trifluoroethanesulfonic acid anions,nonafluorobutanesulfonic acid anions, heptadecafluorooctane-sulfonicacid anions, and camphorsulfonic acid anions. Sulfonium and iodoniumsalts having these anions are especially preferred.

[0194] In the resist composition comprising the onium salt of formula(1), (1a), (1a′) or (1b) as the first photoacid generator according tothe invention, an appropriate amount of the second photoacid generator(C) is 0 to 20 parts, and especially 1 to 10 parts by weight per 100parts by weight of the solids in the composition. The second photoacidgenerators may be used alone or in admixture of two or more. Thetransmittance of the resist film can be controlled by using a (second)photoacid generator having a low transmittance at the exposurewavelength and adjusting the amount of the photoacid generator added.

[0195] In the resist composition according to the invention, there maybe added a compound which is decomposed with an acid to generate anacid, that is, acid-propagating compound. For these compounds, referenceshould be made to J. Photopolym. Sci. and Tech., 8, 43-44, 45-46 (1995),and ibid., 9, 29-30 (1996).

[0196] Examples of the acid-propagating compound includetert-butyl-2-methyl-2-tosyloxymethyl acetoacetate and2-phenyl-2-(tosyloxyethyl)-1,3-dioxolane, but are not limited thereto.Of well-known photoacid generators, many of those compounds having poorstability, especially poor thermal stability exhibit an acid-propagatingcompound-like behavior.

[0197] In the resist composition according to the invention, anappropriate amount of the acid-propagating compound is up to 2 parts,and especially up to 1 part by weight per 100 parts by weight of thesolids in the composition. Excessive amounts of the acid-propagatingcompound makes diffusion control difficult, leading to degradation ofresolution and pattern configuration.

[0198] Component (D)

[0199] The basic compound used as component (D) is preferably a compoundcapable of suppressing the rate of diffusion when the acid generated bythe photoacid generator diffuses within the resist film. The inclusionof this type of basic compound holds down the rate of acid diffusionwithin the resist film, resulting in better resolution. In addition, itsuppresses changes in sensitivity following exposure and reducessubstrate and environment dependence, as well as improving the exposurelatitude and the pattern profile.

[0200] Examples of basic compounds include primary, secondary, andtertiary aliphatic amines, mixed amines, aromatic amines, heterocyclicamines, carboxyl group-bearing nitrogenous compounds, sulfonylgroup-bearing nitrogenous compounds, hydroxyl group-bearing nitrogenouscompounds, hydroxyphenyl group-bearing nitrogenous compounds, alcoholicnitrogenous compounds, amide derivatives, and imide derivatives.

[0201] Examples of the basic compound used herein are described in JP-A2000-194127. Preferred basic compounds are triethylamine,tri-n-propylamine, triisopropylamine, tri-n-butylamine,triisobutylamine, tri-sec-butylamine, tripentylamine, phenethylamine,pyridine, aminopyridine, pyridinium p-toluenesulfonate, monoethanolamine, diethanol amine, triethanol amine, N-ethyldiethanol amine,N,N-diethylethanol amine, triisopropanol amine, 2,2′-iminodiethanol,2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol,4-(2-hydroxyethyl)morpholine, N,N-dimethyl-acetamide,tris(2-methoxyethyl)amine, tris(2-ethoxy-ethyl)amine,tris{2-(methoxymethoxy)ethyl}amine, tris(2-acetyloxyethylamine), andtris(2-propionyloxyethylamine).

[0202] The basic compounds may be used alone or in admixture of two ormore. The basic compound is preferably formulated in an amount of 0 to 2parts, and especially 0.01 to 1 part by weight, per 100 parts by weightof the solids in the resist composition. The use of more than 2 parts ofthe basis compound would result in too low a sensitivity.

[0203] Component (E)

[0204] Illustrative examples of the organic acid derivatives (E) aredescribed in JP-A 2000-194127, though not limited thereto. Preferredorganic acid derivatives include 4-hydroxyphenylacetic acid,2,5-dihydroxyphenylacetic acid, 3,4-dihydroxyphenylacetic acid,1,2-phenylenediacetic acid, 1,3-phenylenediacetic acid,1,4-phenylenediacetic acid, 1,2-phenylenedioxydiacetic acid,1,4-phenylenedipropanoic acid, benzoic acid, salicylic acid,4,4-bis(4′-hydroxy-phenyl)valeric acid, 4-tert-butoxyphenylacetic acid,4-(4′-hydroxyphenyl)butyric acid, 3,4-dihydroxymandelic acid, and4-hydroxymandelic acid. Of these, salicylic acid and4,4-bis(4′-hydroxyphenyl)valeric acid are preferred. They may be usedalone or in admixture of two or more.

[0205] In the resist composition comprising the onium salt according tothe invention, the organic acid derivative is preferably formulated inan amount of up to 5 parts, and especially up to 1 part by weight, per100 parts by weight of the solids in the resist composition. The use ofmore than 5 parts of the organic acid derivative would result in too lowa resolution. Depending on the combination of the other components inthe resist composition, the organic acid derivative may be omitted.

[0206] Component (F)

[0207] In one preferred embodiment, the resist composition furthercontains (F) a compound with a molecular weight of up to 3,000 whichchanges its solubility in an alkaline developer under the action of anacid, that is, a dissolution inhibitor. Typically, a compound obtainedby partially or entirely substituting acid labile substituents on aphenol or carboxylic acid derivative having a molecular weight of up to2,500 is added as the dissolution inhibitor. Examples of the dissolutioninhibitor are described in JP-A 2000-194127, though not limited thereto.

[0208] Preferred dissolution inhibitors include 2,2-bis(4′-(2″-tetrahydropyranyloxy))propane,2,2-bis(4′-tert-butoxycarbonyloxyphenyl)propane, tert-butyl4,4-bis(4′-(2″-tetrahydropyranyloxy)phenyl)valerate, tert-butyl4,4-bis(4′-tert-butoxycarbonyloxyphenyl)valerate, and tert-butyl4,4-bis(4′-tert-butoxycarbonylmethyloxyphenyl)valerate.

[0209] In the resist composition comprising the onium salt according tothe invention, an appropriate amount of the dissolution inhibitor (F) isup to 20 parts, and especially up to 15 parts by weight per 100 parts byweight of the solids in the composition. With more than 20 parts of thedissolution inhibitor, the resist composition becomes less heatresistant because of an increased content of monomer components.

[0210] In a chemical amplification, negative working, resist compositionas well, the onium salt of formula (1), (1a), (1a′) or (1b) according tothe invention may be used as the photoacid generator. This compositionfurther contains an alkali-soluble resin as component (H), examples ofwhich are intermediates of the above-described component (A) though notlimited thereto.

[0211] Examples of the alkali-soluble resin includepoly(p-hydroxystyrene), poly(m-hydroxystyrene),poly(4-hydroxy-2-methylstyrene), poly(4-hydroxy-3-methylstyrene),poly(α-methyl-p-hydroxystyrene), partially hydrogenated p-hydroxystyrenecopolymers, p-hydroxystyrene-α-methyl-p-hydroxystyrene copolymers,p-hydroxystyrene-α-methylstyrene copolymers, p-hydroxystyrene-styrenecopolymers, p-hydroxy-styrene-m-hydroxystyrene copolymers,p-hydroxystyrene-styrene copolymers, p-hydroxystyrene-acrylic acidcopolymers, p-hydroxystyrene-methacrylic acid copolymers,p-hydroxystyrene-methyl methacrylate copolymers,p-hydroxystyrene-acrylic acid-methyl methacrylate copolymers,p-hydroxystyrene-methyl acrylate copolymers,p-hydroxystyrene-methacrylic acid-methyl methacrylate copolymers,poly(methacrylic acid), poly(acrylic acid), acrylic acid-methyl acrylatecopolymers, methacrylic acid-methyl methacrylate copolymers, acrylicacid-maleimide copolymers, methacrylic acid-maleimide copolymers,p-hydroxystyrene-acrylic acid-maleimide copolymers, andp-hydroxystyrene-methacrylic acid-maleimide copolymers as well asdendritic and hyperbranched polymers thereof, but are not limited tothese combinations.

[0212] Preferred are poly(p-hydroxystyrene), partially hydrogenatedp-hydroxystyrene copolymers, p-hydroxystyrene-styrene copolymers,p-hydroxystyrene-acrylic acid copolymers, andp-hydroxystyrene-methacrylic acid copolymers, as well as dendritic andhyperbranched polymers of the foregoing polymers.

[0213] The polymer should preferably have a weight average molecularweight (Mw) of 3,000 to 100,000. Many polymers with Mw of less than3,000 do not perform well and are poor in heat resistance and filmformation. Many polymers with Mw of more than 100,000 give rise to aproblem with respect to dissolution in the resist solvent and developer.The polymer should also preferably have a dispersity (Mw/Mn) of up to3.5, and more preferably up to 1.5. With a dispersity of more than 3.5,resolution is low in many cases. Although the preparation method is notcritical, a poly(p-hydroxystyrene) or similar polymer with a lowdispersity or narrow dispersion can be synthesized by living anionpolymerization.

[0214] To impart a certain function, suitable substituent groups may beintroduced into some of the phenolic hydroxyl and carboxyl groups on theacid labile group-protected polymer. Exemplary and preferred aresubstituent groups for improving adhesion to the substrate, substituentgroups for improving etching resistance, and especially substituentgroups which are relatively stable against acid and alkali and effectivefor controlling such that the dissolution rate in an alkali developer ofunexposed and low exposed areas of a resist film may not become toohigh. Illustrative, non-limiting, substituent groups include2-hydroxyethyl, 2-hydroxypropyl, methoxymethyl, methoxycarbonyl,ethoxycarbonyl, methoxycarbonylmethyl, ethoxycarbonylmethyl,4-methyl-2-oxo-4-oxolanyl, 4-methyl-2-oxo-4-oxanyl, methyl, ethyl,n-propyl, isopropyl, n-butyl, sec-butyl, acetyl, pivaloyl, adamantyl,isobornyl, and cyclohexyl. It is also possible to introduceacid-decomposable substituent groups such as t-butoxycarbonyl andrelatively acid-undecomposable substituent groups such as t-butyl andt-butoxycarbonylmethyl.

[0215] Also contained in the negative resist composition is (I) an acidcrosslinking agent capable of forming a crosslinked structure under theaction of an acid. Typical acid crosslinking agents are compounds havingat least two hydroxymethyl, alkoxymethyl, epoxy or vinyl ether groups ina molecule. Substituted glycoluril derivatives, urea derivatives, andhexa(methoxymethyl)melamine compounds are suitable as the acidcrosslinking agent in the chemically amplified, negative resistcomposition comprising the onium salt according to the invention.Examples include N,N,N′,N′-tetramethoxymethylurea,hexamethoxymethylmelamine, tetraalkoxymethyl-substituted glycolurilcompounds such as tetrahydroxymethyl-substituted glycoluril andtetramethoxy-methylglycoluril, and condensates of phenolic compoundssuch as substituted or unsubstituted bis(hydroxymethylphenol) compoundsand bisphenol A with epichlorohydrin. Especially preferred acidcrosslinking agents are 1,3,5,7-tetraalkoxy-methylglycolurils such as1,3,5,7-tetramethoxymethylglycoluril,1,3,5,7-tetrahydroxymethylglycoluril, 2,6-dihydroxymethyl-p-cresol,2,6-dihydroxymethylphenol, 2,2′,6,6′-tetrahydroxymethyl-bisphenol A,1,4-bis[2-(2-hydroxypropyl)]benzene, N,N,N′,N′-tetramethoxymethylurea,and hexamethoxymethylmelamine. In the resist composition, an appropriateamount of the acid crosslinking agent is about 1 to 25 parts, andespecially about 5 to 15 parts by weight per 100 parts by weight of thesolids in the composition. The acid crosslinking agents may be usedalone or in admixture of two or more.

[0216] In the chemical amplification type, negative working, resistcomposition, (J) an alkali-soluble compound having a molecular weight ofup to 2,500 may be blended. The compound should preferably have at leasttwo phenol and/or carboxyl groups. Illustrative, non-limiting, examplesinclude cresol, catechol, resorcinol, pyrogallol, fluoroglycin,bis(4-hydroxyphenyl)methane, 2,2-bis(4′-hydroxyphenyl)propane,bis(4-hydroxyphenyl)sulfone, 1,1,1-tris(4′-hydroxyphenyl)ethane,1,1,2-tris(4′-hydroxyphenyl)ethane, hydroxybenzophenone,4-hydroxyphenylacetic acid, 3-hydroxyphenylacetic acid,2-hydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid,3-(2-hydroxyphenyl)propionic acid, 2,5-dihydroxyphenylacetic acid,3,4-dihydroxyphenylacetic acid, 1,2-phenylenediacetic acid,1,3-phenylenediacetic acid, 1,4-phenylenediacetic acid,1,2-phenylenedioxydiacetic acid, 1,4-phenylenedipropanoic acid, benzoicacid, salicylic acid, 4,4-bis(4′-hydroxyphenyl)valeric acid,4-tert-butoxyphenylacetic acid, 4-(4-hydroxyphenyl)butyric acid,3,4-dihydroxymandelic acid, and 4-hydroxymandelic acid. Of these,salicylic acid and 4,4-bis(4′-hydroxyphenyl)valeric acid are preferred.They may be used alone or in admixture of two or more. The additionamount is 0 to 20 parts, preferably 2 to 10 parts by weight per 100parts by weight of the solids in the composition although it is notcritical.

[0217] In the resist composition according to the invention, there maybe added such additives as a surfactant for improving coating, and alight absorbing agent for reducing diffuse reflection from thesubstrate.

[0218] Illustrative, non-limiting, examples of the surfactant includenonionic surfactants, for example, polyoxyethylene alkyl ethers such aspolyoxyethylene lauryl ether, polyoxyethylene stearyl ether,polyoxyethylene cetyl ether, and polyoxyethylene oleyl ether,polyoxyethylene alkylaryl ethers such as polyoxyethylene octylphenolether and polyoxyethylene nonylphenol ether, polyoxyethylenepolyoxypropylene block copolymers, sorbitan fatty acid esters such assorbitan monolaurate, sorbitan monopalmitate, and sorbitan monostearate,and polyoxyethylene sorbitan fatty acid esters such as polyoxyethylenesorbitan monolaurate, polyoxyethylene sorbitan monopalmitate,polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitantrioleate, and polyoxyethylene sorbitan tristearate; fluorochemicalsurfactants such as EFTOP EF301, EF303 and EF352 (Tohkem Products K.K.),Megaface F171, F172 and F173 (Dai-Nippon Ink & Chemicals K.K.), FloradeFC430 and FC431 (Sumitomo 3M K.K.), Asahiguard AG710, Surflon S-381,S-382, SC101, SC102, SC103, SC104, SC105, SC106, Surfynol E1004, KH-10,KH-20, KH-30 and KH-40 (Asahi Glass K.K.); organosiloxane polymersKP341, X-70-092 and X-70-093 (Shin-Etsu Chemical Co., Ltd.), acrylicacid or methacrylic acid Polyflow No. 75 and No. 95 (Kyoeisha UshiKagaku Kogyo K.K.). Inter alia, FC430, Surflon S-381 and Surfynol E1004are preferred. These surfactants may be used alone or in admixture.

[0219] In the resist composition according to the invention, thesurfactant is preferably formulated in an amount of up to 2 parts, andespecially up to 1 part by weight, per 100 parts by weight of the solidsin the resist composition.

[0220] In the resist composition according to the invention, a UVabsorber may be added. Exemplary UV absorbers are described in JP-A2000-194127, though not limited thereto.

[0221] An appropriate amount of UV absorber blended is 0 to 10 parts,more preferably 0.5 to 10 parts, most preferably 1 to 5 parts by weightper 100 parts by weight of the base resin.

[0222] For the microfabrication of integrated circuits, any well-knownlithography may be used to form a resist pattern from the chemicalamplification, positive or negative working, resist compositionaccording to the invention.

[0223] The composition is applied onto a substrate (e.g., Si, SiO₂, SiN,SiON, TiN, WSi, BPSG, SOG, organic anti-reflecting film, etc.) by asuitable coating technique such as spin coating, roll coating, flowcoating, dip coating, spray coating or doctor coating. The coating isprebaked on a hot plate at a temperature of 60 to 150° C. for about 1 to10 minutes, preferably 80 to 120° C. for 1 to 5 minutes. The resultingresist film is generally 0.1 to 2.0 μm thick. With a mask having adesired pattern placed above the resist film, the resist film is thenexposed to actinic radiation, preferably having an exposure wavelengthof up to 300 nm, such as UV, deep-UV, electron beams, x-rays, excimerlaser light, γ-rays and synchrotron radiation in an exposure dose ofabout 1 to 200 mJ/cm², preferably about 10 to 100 mJ/cm². The film isfurther baked on a hot plate at 60 to 150° C. for 1 to 5 minutes,preferably 80 to 120° C. for 1 to 3 minutes (post-exposure baking=PEB).

[0224] Thereafter the resist film is developed with a developer in theform of an aqueous base solution, for example, 0.1 to 5%, preferably 2to 3% aqueous solution of tetramethylammonium hydroxide (TMAH) for 0.1to 3 minutes, preferably 0.5 to 2 minutes by conventional techniquessuch as dipping, puddling or spraying. In this way, a desired resistpattern is formed on the substrate. It is appreciated that the resistcomposition of the invention is best suited for micro-patterning usingsuch actinic radiation as deep UV with a wavelength of 254 to 193 nm,electron beams, x-rays, excimer laser light, γ-rays and synchrotronradiation. With any of the above-described parameters outside theabove-described range, the process may sometimes fail to produce thedesired pattern.

EXAMPLE

[0225] Examples of the invention are given below by way of illustrationand not by way of limitation.

Synthesis Example 1

[0226] Synthesis of Sodium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate

[0227] In 100 g of tetrahydrofuran and 80 g of water were dissolved 50 g(0.18 mol) of sodium 2,6-naphtholsulfonate hydrate and 33.8 g (0.18 mol)of p-toluenesulfonyl chloride. With stirring under ice cooling, anaqueous sodium hydroxide solution (containing 7.1 g (0.18 mol) of sodiumhydroxide in 30 g of water) was added dropwise at a temperature below20° C. After the completion of dropwise addition, the reaction solutionwas ripened for 2 hours at room temperature. Dichloromethane, 600 g, wasadded to the reaction solution whereupon sodium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate crystallized. Thecrystals were collected by filtration and washed with 300 g ofdichloromethane. The yield was 90 g (wet).

Synthesis Example 2

[0228] Synthesis of Sodium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0229] In 59 g of tetrahydrofuran and 23 g of water were dissolved 25 g(0.09 mol) of sodium 1,4-naphtholsulfonate hydrate and 16.8 g (0.09 mol)of p-toluenesulfonic acid chloride. With stirring under ice cooling, anaqueous sodium hydroxide solution (containing 3.5 g (0.09 mol) of sodiumhydroxide in 27 g of water) was added dropwise at a temperature below20° C. After the completion of dropwise addition, the reaction solutionwas ripened for 2 hours at room temperature. Dichloromethane, 700 g, wasadded to the reaction solution whereupon sodium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate crystallized. Thecrystals were collected by filtration and washed with 300 g ofdichloromethane. The yield was 48 g (wet).

Synthesis Example 3

[0230] Synthesis of Sodium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0231] In 24 g of tetrahydrofuran and 11 g of water were dissolved 12.3g (0.05 mol) of sodium 1,8-naphtholsulfonate hydrate and 9.5 g (0.05mol) of p-toluenesulfonic acid chloride. With stirring under icecooling, an aqueous sodium hydroxide solution (containing 2 g (0.05 mol)of sodium hydroxide in 9 g of water) was added dropwise at a temperaturebelow 20° C. After the completion of dropwise addition, the reactionsolution was ripened for 2 hours at room temperature. Dichloromethane,100 g, was added to the reaction solution whereupon sodium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate crystallized. Thecrystals were collected by filtration and washed with 300 g ofdichloromethane. The yield was 26 g (wet).

Synthesis Example 4

[0232] Synthesis of Triphenylsulfonium Chloride

[0233] In 400 g of dichloromethane was dissolved 40 g (0.2 mol) ofdiphenyl sulfoxide. With stirring under ice cooling, 65 g (0.6 mol) oftrimethylsilyl chloride was added dropwise at a temperature below 20° C.The reaction solution was ripened at the temperature for 30 minutes.Then, the Grignard reagent which was separately prepared from 14.6 g(0.6 mol) of metallic magnesium, 67.5 g (0.6 mol) of chlorobenzene and168 g of THF was added dropwise at a temperature below 20° C. Thereaction solution was ripened for one hour. At a temperature below 20°C., 50 g of water was added to the reaction solution for terminating thereaction. Further, 150 g of water, 10 g of 12N hydrochloric acid and 200g of diethyl ether were added to the solution.

[0234] The aqueous layer was separated and washed with 100 g of diethylether, obtaining an aqueous solution of triphenylsulfonium chloride.This aqueous solution was subject to the subsequent reaction withoutfurther isolation.

Synthesis Example 5

[0235] Synthesis of 4-tert-butylphenyldiphenylsulfonium Chloride

[0236] The end compound was synthesized as in Synthesis Example 4 exceptthat 4-tert-butylchlorobenzene was used instead of the chlorobenzene inSynthesis Example 4 and the quantity of water for extraction wasincreased.

Synthesis Example 6

[0237] Synthesis of 4-tert-butoxyphenyldiphenylsulfonium Chloride

[0238] The end compound was synthesized as in Synthesis Example 4 exceptthat 4-tert-butoxychlorobenzene was used instead of the chlorobenzene inSynthesis Example 4, dichloromethane containing 5% by weight oftriethylamine was used as the solvent, and the quantity of water forextraction was increased.

Synthesis Example 7

[0239] Synthesis of tris(4-methylphenyl)sulfonium Chloride

[0240] The end compound was synthesized as in Synthesis Example 4 exceptthat bis(4-methylphenyl) sulfoxide was used instead of the phenylsulfoxide in Synthesis Example 4, 4-chlorotoluene was used instead ofthe chlorobenzene, and the quantity of water for extraction wasincreased.

Synthesis Example 8

[0241] Synthesis of tris(4-tert-butylphenyl)sulfonium Chloride

[0242] The end compound was synthesized as in Synthesis Example 4 exceptthat bis(4-tert-butylphenyl) sulfoxide was used instead of the phenylsulfoxide in Synthesis Example 4, 4-tert-butylchlorobenzene was usedinstead of the chlorobenzene, and the quantity of water for extractionwas increased.

Synthesis Example 9

[0243] Synthesis of bis(4-tert-butylphenyl)iodonium Hydrogensulfate

[0244] A mixture of 84 g (0.5 mol) of tert-butylbenzene, 53 g (0.25 mol)of potassium iodate and 50 g of acetic anhydride was stirred under icecooling, and a mixture of 35 g of acetic anhydride and 95 g of conc.sulfuric acid was added dropwise thereto at a temperature below 30° C.The reaction mixture was ripened for 3 hours at room temperature andcooled with ice again, after which 250 g of water was added dropwise forterminating the reaction. The reaction solution was extracted with 400 gof dichloromethane. To the organic layer, 6 g of sodium hydrogensulfitewas added for decoloring. The organic layer was washed with 250 g ofwater three times. After washing, the organic layer was concentrated invacuum, obtaining the crude end product. The product was used in thesubsequent reaction without further purification.

Synthesis Example 10

[0245] Synthesis of triphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate

[0246] The sodium 6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonatecrude product obtained in Synthesis Example 1, 90 g, was added to theaqueous triphenylsulfonium chloride solution obtained in SynthesisExample 4 and 400 g of dichloromethane, which was stirred for one hourat room temperature. The organic layer was separated, washed with 400 gof water, and concentrated in vacuum. The residue, 130 g, was purifiedby recrystallization from diethyl ether, obtaining the end product,triphenylsulfonium 6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonateas crystals in an amount of 100 g (yield 79%).

[0247] The triphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate thus obtained wasanalyzed by nuclear magnetic resonance (NMR) spectroscopy and infrared(IR) absorption spectroscopy, with the results shown below.

[0248] 3057, 1597, 1498, 1477, 1448, 1367, 1228, 1201, 1178, 1140, 1119,1090, 1230, 995, 922, 881, 843, 812, 773, 762, 731, 669, 648, 623, 604

[0249] Elemental analysis: C₃₅H₂₈O₆S₃ (%)

[0250] Calcd.C 65.6H 4.4

[0251] Found C 66.OH 4.5

Synthesis Example 11

[0252] Synthesis of triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0253] The sodium 4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonatecrude product obtained in Synthesis Example 2, 48 g, was added to onehalf of the aqueous triphenylsulfonium chloride solution obtained inSynthesis Example 4 and 200 g of dichloromethane, which was stirred forone hour at room temperature. The organic layer was separated, washedwith 200 g of water, and concentrated in vacuum. The residue, 60 g, waspurified by recrystallization from diethyl ether, obtaining the endproduct, triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate as crystals in anamount of 49 g (yield 76%).

[0254] The triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate thus obtained wasanalyzed by NMR and IR spectroscopy, with the results shown below.

[0255] 3059, 1475, 1446, 1367, 1228, 1209, 1108, 1159, 1122, 1093, 1038,1034, 1016, 947, 854, 810, 789, 760, 721, 687, 681, 629

[0256] Elemental analysis: C₃₅H₂₈O₆S (%)

[0257] Calcd.C 65.6H 4.4

[0258] Found C 65.9H 4.2

Synthesis Example 12

[0259] Synthesis of Triphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0260] The sodium 8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonatecrude product obtained in Synthesis Example 3, 26 g, was added to aquarter of the aqueous triphenylsulfonium chloride solution obtained inSynthesis Example 4 and 100 g of dichloromethane, which was stirred forone hour at room temperature. The organic layer was separated, washedwith 100 g of water, and concentrated in vacuum. The residue, 32 g, waspurified by recrystallization from diethyl ether, obtaining the endproduct, triphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate as crystals in anamount of 25 g (yield 43%).

[0261] The triphenylsulfonium8-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate thus obtained wasanalyzed by NMR and IR spectroscopy, with the results shown below.

[0262] 3086, 3059, 1597, 1477, 1448, 1356, 1225, 1174, 1105, 1086, 1041,1014, 939, 835, 814, 750, 685, 654, 623

[0263] Elemental analysis: C₃₅H₂₈O₆S₃ (%)

[0264] Calcd.C 65.6H 4.4

[0265] Found C 66.1H 4.0

Synthesis Example 13

[0266] Synthesis of 4-tert-butylphenyldiphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate

[0267] The end compound was synthesized as in Synthesis Example 10except that the 4-tert-butylphenyldiphenylsulfonium chloride inSynthesis Example 5 was used instead of the triphenylsulfonium chloridein Synthesis Example 10.

Synthesis Example 14

[0268] Synthesis of 4-tert-butoxyphenyldiphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate

[0269] The end compound was synthesized as in Synthesis Example 10except that the 4-tert-butoxyphenyldiphenylsulfonium chloride inSynthesis Example 6 was used instead of the triphenylsulfonium chloridein Synthesis Example 10.

Synthesis Example 15

[0270] Synthesis of tris(4-methylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0271] The end compound was synthesized as in Synthesis Example 10except that the tris(4-methylphenyl)sulfonium chloride in SynthesisExample 7 was used instead of the triphenylsulfonium chloride inSynthesis Example 11.

Synthesis Example 16

[0272] Synthesis of tris(4-tert-butylphenyl)sulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0273] The end compound was synthesized as in Synthesis Example 10except that the tris(4-tert-butylphenyl)sulfonium chloride in SynthesisExample 8 was used instead of the triphenylsulfonium chloride inSynthesis Example 11.

Synthesis Example 17

[0274] Synthesis of bis(4-tert-butylphenyl)iodonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0275] The end compound was synthesized as in Synthesis Example 10except that the bis(4-tert-butylphenyl)iodonium chloride in SynthesisExample 9 and 200 g of water were used instead of the triphenylsulfoniumchloride in Synthesis Example 11.

[0276] For further reference, the synthesis of branched polymers isdescribed below.

Reference Example 1

[0277] Synthesis of Tri-branched poly(p-hydroxystyrene)

[0278] A 1-liter flask was charged with 500 ml of tetrahydrofuran as asolvent and 0.01 mol of sec-butyl lithium as an initiator. To thesolution at −78° C. was added 40 g of p-tert-butoxystyrene. Withstirring, polymerization reaction was effected for 30 minutes. Thereaction solution turned red. For producing a branched polymer, 0.005mol of p-chloromethylstyrene was added to the reaction solutionwhereupon reaction was effected for 5 minutes. The reaction solution wasred. Further 20 g of p-tert-butoxystyrene was added. With stirring,polymerization reaction was effected for 30 minutes. Polymerization wasstopped by adding 0.1 mol of methanol to the reaction solution.

[0279] For purifying the polymer, the reaction mixture was poured intomethanol whereupon the polymer precipitated. Separation and dryingyielded 44 g of a white polymer which was tri-branchedpoly(p-tert-butoxystyrene).

[0280] For producing tri-branched poly(p-hydroxystyrene), 44 g of theabove tri-branched poly(p-tert-butoxystyrene) was dissolved in 400 ml ofacetone. A minor amount of conc. hydrochloric acid was added to thesolution at 60° C., which was stirred for 7 hours. The reaction solutionwas poured into water whereupon the polymer precipitated. Washing anddrying yielded 25 g of a white polymer. Since a peak attributable totert-butyl group was not found in GPC and proton-NMR analysis, thispolymer was confirmed to be tri-branched poly(p-hydroxystyrene) having anarrow molecular weight distribution.

[0281] The polymer had a weight average molecular weight (Mw) of 8,500as determined by GPC using polystyrene standard and a dispersity (Mw/Mn)of 1.10.

Reference Example 2

[0282] Synthesis of Nona-branched poly(p-hydroxystyrene)

[0283] A 2-liter flask was charged with 1000 ml of tetrahydrofuran as asolvent and 0.06 mol of sec-butyl lithium as an initiator. To thesolution at −78° C. was added 60 g of p-tert-butoxystyrene. Withstirring, polymerization reaction was effected for 30 minutes. Thereaction solution turned red. For producing a tri-branched polymer, 0.03mol of p-chloromethylstyrene was added to the reaction solutionwhereupon reaction was effected for 5 minutes. Then 30 g ofp-tert-butoxystyrene was added to the reaction solution, which wasstirred for 30 minutes for polymerization. The reaction solution wasred. For producing penta-branched polymer, 0.015 mol ofp-chloromethylstyrene was added to the reaction solution whereuponreaction was effected for 5 minutes. Then 15 g of p-tert-butoxystyrenewas added to the reaction solution, which was stirred for 30 minutes forpolymerization. The reaction solution was red. Finally for producingnona-branched polymer, 0.0075 mol of p-chloromethylstyrene was added tothe reaction solution whereupon reaction was effected for 5 minutes.Then 7.5 g of p-tert-butoxystyrene was added to the reaction solution,which was stirred for 30 minutes for polymerization. The reactionsolution was red. Polymerization was stopped by adding 0.1 mol of carbondioxide gas to the reaction solution.

[0284] For purifying the polymer, the reaction mixture was poured intomethanol whereupon the polymer precipitated. Separation and dryingyielded 99 g of a white polymer which was nona-branchedpoly(p-tert-butoxystyrene).

[0285] For converting to nona-branched poly(p-hydroxystyrene), 99 g ofthe above nona-branched poly(p-tert-butoxystyrene) was dissolved in 1000ml of acetone. A minor amount of conc. hydrochloric acid was added tothe solution at 60° C., which was stirred for 7 hours. The reactionsolution was poured into water whereupon the polymer precipitated.Washing and drying yielded 66 g of a white polymer. Since a peakattributable to tert-butyl group was not found on GPC and proton-NMRanalysis, this polymer was confirmed to be nona-branchedpoly(p-hydroxystyrene) having a narrow molecular weight distribution.

[0286] The polymer had a weight average molecular weight (Mw) of 11,000as determined by GPC using polystyrene standard and a dispersity (Mw/Mn)of 1.25.

Examples 1-24 and Comparative Examples 1-3

[0287] Resist materials were prepared in accordance with the formulationshown in Tables 1 to 3. The components used are shown below.

[0288] Polymer A: poly(p-hydroxystyrene) in which hydroxyl groups areprotected with 15 mol % of 1-ethoxyethyl groups and 15 mol % oftert-butoxycarbonyl groups, having a weight average molecular weight of12,000.

[0289] Polymer B: poly(p-hydroxystyrene) in which hydroxyl groups areprotected with 10 mol % of 1-ethoxyethyl groups and 15 mol % oftert-butoxycarbonyl groups, having a weight average molecular weight of11,000.

[0290] Polymer C: nano-branched poly(p-hydroxystyrene) in which hydroxylgroups are protected with 20 mol % of 1-ethoxyethyl groups and 5 mol %of tert-butoxycarbonyl groups, having a weight average molecular weightof 14,000.

[0291] Polymer D: poly(p-hydroxystyrene) in which hydroxyl groups areprotected with 25 mol % of 1-ethoxyethyl groups and crosslinked with 3mol % of 1,2-propane diol divinyl ether, having a weight averagemolecular weight of 13,000.

[0292] Polymer E: tri-branched poly(p-hydroxystyrene) in which hydroxylgroups are protected with 30 mol % of 1-ethoxyethyl groups, having aweight average molecular weight of 11,000.

[0293] Polymer F: poly(p-hydroxystyrene) in which hydroxyl groups areprotected with 10 mol % of 1-ethoxyethyl groups and 3 mol % oftert-butoxycarbonyl groups and crosslinked with 3mol % of 1,2-propanediol divinyl ether, having a weight average molecular weight of 15,000.

[0294] Polymer G: poly(p-hydroxystyrene) in which hydroxyl groups areprotected with 15 mol % of 1-ethoxyethyl groups and 10 mol % oftert-butoxycarbonyl groups and crosslinked with 3mol % of 1,2-propanediol divinyl ether, having a weight average molecular weight of 13,000.

[0295] Polymer H: p-hydroxystyrene/1-ethylcyclopentyl methacrylatecopolymer having a compositional ratio (molar ratio) of 70:30, andhaving a weight average molecular weight of 11,000.

[0296] Polymer I: p-hydroxystyrene/1-ethylcyclopentyl acrylate copolymerhaving a compositional ratio (molar ratio) of 65:35, and having a weightaverage molecular weight of 14,000.

[0297] Polymer J: the same as Polymer G further containing 5% by weightof styrene and having a weight average molecular weight of 12,000.

[0298] Polymer K: p-hydroxystyrene/1-ethylcyclopentyl methacrylatecopolymer having a compositional ratio (molar ratio) of 70:30, phenolichydroxyl groups in the p-hydroxystyrene being crosslinked with 2 mol %of 1,2-propane diol divinyl ether, the copolymer having a weight averagemolecular weight of 13,000.

[0299] Polymer L: p-hydroxystyrene/1-ethylcyclopentylmethacrylate/p-tert-butoxystyrene copolymer having a compositional ratio(molar ratio) of 60:30:10, and having a weight average molecular weightof 12,000.

[0300] Polymer M: p-hydroxystyrene/1-ethylcyclopentylmethacrylate/tert-butoxycarbonyloxystyrene copolymer having acompositional ratio (molar ratio) of 70:20:10, phenolic hydroxyl groupsin the p-hydroxystyrene being crosslinked with 1 mol % of 1,2-propanediol divinyl ether, the copolymer having a weight average molecularweight of 12,000.

[0301] Polymer N: poly(p-hydroxystyrene) in which hydroxyl groups areprotected with 8 mol % of acetyl groups, having a weight averagemolecular weight of 8,000.

[0302] PAG1: triphenylsulfonium4-(4′-methylphenylsulfonyloxy)naphthalene-1-sulfonate

[0303] PAG2: 4-tert-butoxyphenyldiphenylsulfonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate

[0304] PAG3: bis(4-tert-butylphenyl)iodonium6-(4′-methylphenylsulfonyloxy)naphthalene-2-sulfonate

[0305] PAG4: (4-tert-butoxyphenyl)diphenylsulfonium p-toluenesul-fonate

[0306] PAG5: (4-tert-butoxyphenyl)diphenylsulfonium 10-camphorsulfonate

[0307] PAG6: bis(tert-butylsulfonyl)diazomethane

[0308] PAG7: bis(cyclohexylsulfonyl)diazomethane

[0309] PAG8: bis(2,4-dimethylphenylsulfonyl)diazomethane

[0310] PAG9: N-10-camphorsulfonyloxysuccinimide

[0311] Crosslinker A: 1,3,5,7-tetramethoxymethylglycoluril

[0312] Dissolution inhibitor A:bis(4-(2′-tetrahydropyranyloxy)phenyl)methane

[0313] Basic compound A: tri-n-butylamine

[0314] Basic compound B: tris(2-methoxyethyl)amine

[0315] Organic acid derivative A: 4,4-bis(4′-hydroxyphenyl)valeric acid

[0316] Organic acid derivative B: salicylic acid

[0317] Surfactant A: FC-430 (Sumitomo 3M K.K.)

[0318] Surfactant B: Surflon S-381 (Asahi Glass K.K.)

[0319] UV absorber A: 9,10-dimethylanthracene

[0320] Solvent A: propylene glycol methyl ether acetate

[0321] Solvent B: ethyl lactate TABLE 1 Composition Example (pbw) 1 2 34 5 6 7 8 9 10 11 12 Polymer A 80 40 40 Polymer B 80 Polymer C 80Polymer D 80 40 Polymer E 80 Polymer F 80 Polymer G 80 40 Polymer H 80Polymer I 80 Polymer J 80 Polymer K Polymer L Polymer M Polymer N PAG1 22 2 1 2 2 1 PAG2 2 1 2 PAG3 2 1 2 PAG4 1 1 PAG5 2 1 2 2 2 PAG6 2 0.5 1 1PAG7 2 0.5 PAG8 1 0.25 2 PAG9 0.5 Crosslinker A Dissolution inhibitor ABasic compound A 0.125 0.125 0.125 0.06 0.125 0.125 0.1 0.125 Basiccompound B 0.125 0.125 0.06 0.025 0.125 0.125 Organic acid 1 1 1 1 1 10.25 1 1 1 1 derivative A Organic acid 0.5 0.25 derivative B SurfactantA 0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25 Surfactant B 0.25 0.25 0.250.25 UV absorber A Solvent A 280 280 388 280 388 280 280 280 280 388 280280 Solvent B 105 105 105 105 105 105 105 105 105

[0322] TABLE 2 Composition Example (pbw) 13 14 15 16 17 18 19 20 21 2223 24 Polymer A 70 50 50 50 Polymer B Polymer C 20 20 50 Polymer D 10 40Polymer E 40 Polymer F Polymer G 10 10 40 20 Polymer H 40 Polymer I 1010 10 40 10 Polymer J 40 Polymer K 80 40 Polymer L 40 Polymer H 80Polymer N 80 PAG1 2 1 1 2 2 PAG2 1 1 2 PAG3 2 1 2 2 2 4 PAG4 1 1 1 1PAG5 1 1 1 2 2 2 1 PAG6 1 1 1 0.5 1 PAG7 1 0.25 0.5 PAG8 0.5 PAG9 0.5Crosslinker A 10 Dissolution 2 2 inhibitor A Basic compound A 0.1250.075 0.125 0.125 0.125 Basic compound B 0.125 0.125 0.05 0.125 0.1250.125 0.125 0.125 Organic acid 1 1 0.5 derivative A Organic acid 1 1 0.51 0.5 1 0.5 1 derivative B Surfactant A 0.25 0.125 0.25 0.25 0.25 0.250.125 Surfactant B 0.25 0.25 0.125 0.25 0.125 0.25 0.25 UV absorber A0.25 Solvent A 280 388 388 388 280 280 388 388 280 280 388 388 Solvent B105 105 105 105 105

[0323] TABLE 3 Composition Comparative Example (pbw) 1 2 3 Polymer A 80Polymer D 80 Polymer G 80 PAG4 1 PAG8 2 2 PAG9 1 2 Organic acidderivative A Organic acid derivative B 1 Basic compound A 0.125 0.125Basic compound B 0.125 Surfactant A 0.25 0.25 Surfactant B 0.25 SolventA 388 388 388

[0324] The resist materials thus obtained were each filtered through a0.2-μm Teflon® filter, thereby giving resist solutions. These resistsolutions were spin-coated onto silicon wafers, then baked at 100° C.for 90 seconds on a hot plate to give resist films having a thickness of0.6 pm.

[0325] The resist films were exposed using an excimer laser scannerNSR2005EX (Nikon Corp., NA 0.5), then baked (PEB) at 110° C. for 90seconds, and developed with a solution of 2.38% tetramethylammoniumhydroxide in water, thereby giving positive patterns (Examples 1 to 23and Comparative Examples 1-3) or negative patterns (Example 24). Theresulting resist patterns were evaluated as described below.

[0326] Resist Pattern Evaluation

[0327] The exposure dose which provided a 1:1 resolution at the top andbottom of a 0.24-μm line-and-space pattern was the optimum exposure dose(sensitivity Eop). The minimum line width of a line-and-space patternwhich was ascertained separate at this dose was the resolution of a testresist. The shape in cross section of the resolved resist pattern wasexamined under a scanning electron microscope.

[0328] The PED stability of a resist was evaluated by effectingpost-exposure bake (PEB) after 24 hours of holding from exposure at theoptimum dose and determining a variation in line width (or groove widthfor the negative resist). The less the variation, the greater is the PEDstability.

[0329] The results of resist pattern evaluation are shown in Table 4.

[0330] Other Evaluation

[0331] The solubility of resist material in a solvent mixture wasexamined by visual observation and in terms of clogging upon filtration.

[0332] With respect to the applicability of a resist solution, unevencoating was visually observed. Additionally, using a film gage CleanTrack Mark 8 (Tokyo Electron K.K.), the thickness of a resist film on acommon wafer was measured at different positions, based on which avariation from the desired coating thickness (0.6 μm) was calculated.The applicability was rated “good” when the variation was within 0.5%(that is, within 0.003 pm), “unacceptable” when the variation was frommore than 0.5% to 1%, and “poor” when the variation was more than 1%.

[0333] Storage stability was judged in terms of foreign matterprecipitation or sensitivity change during aging. After the resistsolution was aged for 100 days at the longest, the number of particlesof greater than 0.3 μm per ml of the resist solution was counted bymeans of a particle counter KL-20A (Rion K.K.), and the foreign matterprecipitation was determined “good” when the number of particles is notmore than 5. Also, the sensitivity change was rated “good” when a changewith time of sensitivity (Eop) was within 5% from that immediately afterpreparation, and “poor” when the change is more than 5%.

[0334] Debris appearing on the developed pattern was observed under ascanning electron microscope (TDSEM) model S-7280H (Hitachi Ltd.). Theresist film was rated “good” when the number of foreign particles was upto 10 per 100 μm², “unacceptable” when from 11 to 15, and “poor” whenmore than 15.

[0335] Debris left after resist peeling was examined using a surfacescanner Surf-Scan 6220 (Tencol Instruments). A resist-coated 8-inchwafer was subjected to entire exposure rather than patterned exposure,processed in a conventional manner, and developed with a 2.38% TMAHsolution before the resist film was peeled off (only the resist film inthe exposed area was peeled). After the resist film was peeled, thewafer was examined and rated “good” when the number of foreign particlesof greater than 0.20 μm was up to 100, “unacceptable” when from 101 to150, and “poor” when more than 150.

[0336] The results are shown in Table 5. TABLE 4 24 hr PED dimensionalSensitivity Resolution stability (mJ/cm²) (μm) Profile (nm) Example 1 280.21 rectangular −6 Example 2 29 0.20 rectangular −8 Example 3 227 0.19rectangular −10 Example 4 30 0.20 rectangular −8 Example 5 29 0.19rectangular −8 Example 6 25 0.19 rectangular −8 Example 7 27 0.20rectangular −7 Example 8 26 0.20 rectangular −10 Example 9 29 0.20rectangular −5 Example 10 28 0.20 rectangular 8 Example 11 29 0.20rectangular −8 Example 12 30 0.20 rectangular −9 Example 13 27 0.19rectangular 5 Example 14 29 0.20 rectangular −8 Example 15 30 0.20rectangular −7 Example 16 28 0.20 rectangular −4 Example 17 27 0.20rectangular −8 Example 18 28 0.19 rectangular 4 Example 19 27 0.20rectangular −4 Example 20 26 0.19 rectangular 5 Example 21 26 0.21rectangular −5 Example 22 27 0.20 rectangular 8 Example 23 25 0.19rectangular 8 Example 24 26 0.21 rectangular 4 (negative) Comparative 350.22 forward −30 Example 1 tapered Comparative 34 0.23 rounded −30Example 2 head Comparative 34 0.23 forward 30 Example 3 tapered

[0337] TABLE 5 100 day Debris after Debris Dissolu- Applica- storagedevelopment after tion tion stability (patterning) peeling Example 1good good good good good Example 2 good good good good good Example 3good good good good good Example 4 good good good good good Example 5good good good good good Example 6 good good good good good Example 7good good good good good Example 8 good good good good good Example 9good good good good good Example 10 good good good good good Example 11good good good good good Example 12 good good good good good Example 13good good good good good Example 14 good good good good good Example 15good good good good good Example 16 good good good good good Example 17good good good good good Example 18 good good good good good Example 19good good good good good Example 20 good good good good good Example 21good good good good good Example 22 good good good good good Example 23good good good good good Example 24 good good good good good Comparativegood good <30 days poor poor Example 1 (sensitivity changed) Comparativegood good <30 days good un- Example 2 (sensitivity accept- changed) ableComparative un- good good poor poor Example 3 accept- able

[0338] There have been described specific onium salts having anarylsulfonyloxynaphthalenesulfonate anion. Since thenaphthalenesulfonate anion of the onium salt has a sulfonate groupincorporated therein, chemical amplification type resist compositionscomprising the onium salts as the photoacid generator have manyadvantages including improved resolution, improved focus latitude,minimized line width variation or shape degradation even on long-termPED, minimized debris left after coating, development and peeling, andimproved pattern profile after development. Because of high resolution,the compositions are suited for microfabrication, especially by deep UVlithography.

[0339] Japanese Patent Application No. 2000-322189 is incorporatedherein by reference.

[0340] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. An onium salt of the following general formula (1):

wherein R¹ is a substituted or unsubstituted aryl group of 6 to 14carbon atoms, R² which may be the same or different is hydrogen or asubstituted or unsubstituted, straight, branched or cyclic alkyl groupof 1 to 6 carbon atoms, R⁰ is a hydroxyl, alkoxy, halogen or nitrogroup, p is 1 or 2, q and r each are 0, 1 or 2, R³ which may be the sameor different is a substituted or unsubstituted, straight, branched orcyclic alkyl group of 1 to 10 carbon atoms or substituted orunsubstituted aryl group of 6 to 14 carbon atoms, M is a sulfur oriodine atom, and “a” is equal to 3 when M is sulfur and equal to 2 whenM is iodine.
 2. A sulfonium salt of the following general formula (1a):

wherein R¹, R², R⁰, p, q, r and R³ are as defined above.
 3. A sulfoniumsalt of the following general formula (1a′):

wherein R¹, R², R⁰, p, q, r and R³ are as defined above, G is an acidlabile group having an oxygen atom attached thereto or R²O— or (R²)₂N—,g is an integer of 0 to 4, h is an integer of 1 to 5, g+h =5, e is aninteger of 1 to 3, f is an integer of 0 to 2, and e+f=3.
 4. Thesulfonium salt of claim 3 wherein the acid labile group is selected fromthe class consisting of tert-butoxy, tert-amyloxy,tert-butoxycarbonyloxy, tert-butoxycarbonylmethyloxy, 1-ethoxyethoxy,tetrahydropyranyloxy, tetrahydrofuranyloxy, trimethylsilyloxy, and1-ethylcyclopentyloxy groups.
 5. A iodonium salt of the followinggeneral formula (lb):

wherein R¹, R², R⁰, p, q, and r are as defined above.
 6. A photoacidgenerator for a chemical amplification type resist compositioncomprising the onium salt of claim
 1. 7. A chemical amplification typeresist composition comprising (A) a resin which changes its solubilityin an alkaline developer under the action of an acid, and (B) thephotoacid generator of claim 6 which generates an acid upon exposure toradiation.
 8. A chemical amplification type resist compositioncomprising (A) a resin which changes its solubility in an alkalinedeveloper under the action of an acid, (B) the photoacid generator ofclaim 6 which generates an acid upon exposure to radiation, and (C) acompound capable of generating an acid upon exposure to radiation, otherthan component (B).
 9. The resist composition of claim 7 wherein theresin (A) has such substituent groups having C—O—C linkages that thesolubility in an alkaline developer changes as a result of scission ofthe C—O—C linkages under the action of an acid.
 10. The resistcomposition of claim 7 further comprising (D) a basic compound.
 11. Theresist composition of claim 7 further comprising (E) a carboxylgroup-containing compound.
 12. A process for forming a pattern,comprising the steps of: applying the resist composition of claim 7 ontoa substrate to form a coating, heat treating the coating and exposingthe coating to high energy radiation with a wavelength of up to 300 nmor electron beam through a photo-mask, optionally heat treating theexposed coating, and developing the coating with a developer.